Gemara

(R. Yehoshua ben Levi): If one sees a friend for the first time in 30 days, he blesses Shehecheyanu;

If one sees a friend for the first time in 12 months, he says "Baruch Mechayeh ha'Mesim."

(Rav): A Mes is not forgotten until 12 months -- "Nishkachti k'Mes mi'Lev Hayisi ki'Chli Oved."

Rav Papa and Rav Huna brei d'Rav Yehoshua encountered Rav Chanina brei d'Rav Ika. They told him "we can make two Berachos for seeing you - 'blessed is He who apportioned from His wisdom to those who fear Him,' and Shehecheyanu."

59b (Beraisa): The rule is, if it is [only] his, he blesses Shehecheyanu. If it belongs to him and someone else, he blesses ha'Tov veha'Metiv.

Question: Sometimes one says ha'Tov veha'Metiv even if he has no partner!

(Beraisa): If a man was told that his wife gave birth to a boy, he blesses ha'Tov veha'Metiv.

Answer: There, also his wife is happy to have a boy.

Rishonim

R. Yonah and Rosh (43b DH ha'Ro'eh and 9:9): One blesses only for a dear friend, for whom he has Simchah and pleasure when he sees him.

R. Yonah (DH l'Acher): If he had not seen him for 12 months, he says "Baruch Mechayeh ha'Mesim." This is because he was forgotten from the heart like a Mes, just like a person despairs from a lost Kli after 12 months - "Nishkachti k'Mes mi'Lev Hayisi ki'Chli Oved."

Question: If many get pleasure from seeing a person, do they bless ha'Tov veha'Metiv?

Answer (Rashba Teshuvah 4:77): We do not say ha'Tov veha'Metiv whenever many benefit. If so, one would bless ha'Tov veha'Metiv even for new gourds! Rather, it is only for something that he gets use and pleasure from it, and also others do, e.g. rain, inheriting relatives, or other wines that also others will drink from. We do not find this merely for pleasure, e.g. seeing new fruits. The Gemara asked why one blesses ha'Tov veha'Metiv when he hears that his wife gave birth to a boy, even though he has no partner. It answered that also his wife is happy. It should suffice that his household get pleasure and are happy. Everyone is happy when boys are born! Rather, it must be pleasure of something useful. A son is useful for his parents, to support them in old age and to bury them. Also, he is like a leg of his parents. Everyone desires heirs.

Rashba (Teshuvah 4:76): If Ploni never saw Almoni, but they sent letters to each other, and now he sees him and gets pleasure, he need not bless. If one would bless on everything he gets Hana'ah from, there would be many Berachos. The Gemara said to bless only for a friend he is frequent with. If one blesses on one whom he never saw, this distinction does not apply. For a friend one did not see for 30 days, he blesses Shehecheyanu. If he did not see him for 12 months, he says "Baruch Mechayeh ha'Mesim." If he never saw him, all the more so 12 months have passed! Rather, the Berachah is only for someone he saw, and then did not see him for a while. If 12 months passed, it is as if he departed from him and died, and came back to life.

R. Yonah (1a DH Ela): If (before night) one read Keri'as Shema in the Beis ha'Keneses with its Berachos, he repeats it after Tzeis ha'Kochavim in his house with intent to be Yotzei. Rav Amram says that he blesses Asher Kidshanu b'Mitzvosav v'Tzivanu Likro Keri'as Shema. This is wrong. We do not find such a Berachah anywhere. It is better to say Ahavas Olam. We find that this exempts even for reading verses or learning [oral] Torah. Even though he did not bless Ma'ariv Aravim now, and it is not Samuch l'Chavertah (immediately after another Berachah), since in its [normal] place it is Samuch l'Chavertah, we are not concerned if when he says it now for Keri'as Shema it does not begin with Baruch. We find that Tefilas ha'Derech does not begin with Baruch, but it closes Shome'a Tefilah. Since in Shemoneh Esre, Shome'a Tefilah is Samuch l'Chavertah, we are not concerned if now it is not Samuch.

Poskim

Shulchan Aruch (OC 225:1): If one sees a friend after 30 days, he blesses Shehecheyanu.

Magen Avraham (1): Even if also others enjoy seeing him, he does not bless ha'Tov veha'Metiv, for this is not Tovah (benefit). It is only Simchah.

Mishnah Berurah (1): If one sees a Chacham Yisrael, he blesses "...who apportioned from His wisdom...', and also Shehecheyanu if he had not seen him for 30 days.

Kaf ha'Chayim (5): We say the Berachah on Chachmei Yisrael without Shem and Malchus.

Hilchos Ketanos (1:213): If one receives a letter from his dear friend and finds out that his situation is good, perhaps he may audibly bless ha'Tov veha'Metiv. If one comes from afar to prostrate on his father's grave, perhaps he blesses Shehecheyanu and Dayan ha'Emes. The Rashba said that there is no difference between males and females. This refers [only] to his daughter, sister, mother or wife.

Sha'arei Teshuvah (1): According to this, surely a woman blesses only on her father, brother, son or husband.

Kaf ha'Chayim (2): One blesses on women only if they are relatives that he is used to them. He does not bless on other women, lest he come to [lustful] thoughts about them. Yafeh l'Lev says that a distinguished person should not bless on his wife, and even on his daughter the custom is not to bless.

Hilchos Ketanos (1:220, cited in Birkei Yosef 3): If a friend left the city, and within 30 days he received a letter from him, or people told him about his Shalom (wellbeing) even so he blesses Shehecheyanu, which is for seeing his face. However, one does not bless Mechayeh Mesim (if he received a letter or from him or heard about his Shalom within the 12 months).

Ha'aros on Birkei Yosef (1): Mishpetai Tzedek says that a letter does not exempt from the Berachah. Halichos Olam (2 p.184) says that Hilchos Ketanos' opinion is primary; Safek Berachos Lehakel. Ta'alumos Lev and Yalkut Yosef say that all the more so if one spoke with him on the phone, he does not bless; the same applies to Shehecheyanu. Halichos Olam says that it exempts only from Mechayeh Mesim, but not from Shehecheyanu, which is for Simchah. Maharam Azulai (the Birkei Yosef's grandson) equates Shehecheyanu to Mechayeh Mesim, but says that Hilchos Ketanos did not.

Note: Yalkut Yosef (Kitzur Shulchan Aruch 223:20,21) holds like Halichos Olam. He blesses Shehecheyanu as long as he has Simchah upon seeing him.

Sha'arei Teshuvah (1): This connotes that even if people came and told him about Ploni's Shalom, he does not bless. Also the Birkei Yosef connotes like this. This requires investigation.

Mishnah Berurah (2): If he received letters from him or people told him about him, Acharonim argue about this. We are lenient (not to bless Safek Berachos).

Birkei Yosef (1): There is no distinction whether one sees someone greater or smaller than himself.

Shulchan Aruch (ibid.): After 12 months, he blesses "Mechayeh Mesim."

Magen Avraham (2): When he blesses Mechayeh Mesim, he does not bless Shehecheyanu.

Birkei Yosef (3): It is not clear whether one blesses Shehecheyanu along with Mechayeh Mesim. Zichron Moshe, the Maharshal and Acharonim say that he does not.

Panim Me'iros (1:66 DH Ma'aseh, DH b'Tur, cited in R. Akiva Eiger): I was unsure whether one blesses Mechayeh Mesim with Shem and Malchus, for the text of this Berachah is in Shemoneh Esre, and there it has no Shem and Malchus. Tosfos explained that Magen Avraham is like Shem and Malchus, and the Berachos of Shemoneh Esre (after the first) are Samuch l'Chavertah. If so, always when blessing on a friend, it is without Shem and Malchus. I learn from R. Yonah. He rules to say Ahavas Olam before repeating Keri'as Shema, even though now it is not Samuch, since in Birkos Keri'as Shema it is Samuch. He learned from Tefilas ha'Derech, which does not begin with Baruch, since in Shemoneh Esre it is Samuch. Also the Magen Avraham (59:1) says that the order of the Berachos is not Me'akev. One may say the second Berachah before the first. Even though it does not begin with Baruch, since it was enacted Samuch l'Chavertah, one can read it by itself without Shem and Malchus. The Rashba says because it is a short Berachah. This requires investigation. If so (NOTE: both according to R. Yonah and the Rashba - PF), in our case one need not mention Malchus.

Shiyurei Berachah (1): He blesses Mechayeh Mesim. I.e. it is a full Berachah with Shem and Malchus, unlike Panim Me'iros. His proofs are not proofs. Sefer ha'Pardes explicitly says [that it is with Shem and Malchus].

Mishnah Berurah (3): All these Berachos are with Shem and Malchus, even Mechayeh Mesim (Magen Giborim and the other Acharonim, unlike Panim Me'iros).

Kaf ha'Chayim (6): Ben Ish Chai says that the custom is not to bless Mechayeh Mesim, for people do not like hearing others say that they died, and to bless Shehecheyanu without Shem and Malchus. Where there is no custom, one should bless Shehecheyanu without Shem and Malchus, and (when it applies) Mechayeh Mesim in his heart.

Mishnah Berurah (4): The Maharsha explains that each year one is judged on Rosh Hashanah and Yom Kipur, to die or live. One says Baruch Mechayeh Mesim because he was saved from a judgment of death on Rosh Hashanah and Yom Kipur.

Note: I do not understand how this depends on 12 months. Ha'arah 21 in the Oz v'Hadar edition of Mishnah Berurah says that the Maharsha agrees with R. Yonah, that one blesses because he was forgotten from the heart. The Maharsha merely explains why the text is Mechayeh Mesim.

Halichos Shlomo (Orchos Halachah 23:47): In a leap year, if one saw a friend after more than 12 months, he blesses, even though Rosh Hashanah and Yom Kipur did not come in between.

Shulchan Aruch (ibid.): This is if he is very dear to him, and he is happy to see him.

Gra: We learn from Rav Papa and Rav Huna. Why did they need to tell Rav Chanina that they can bless also Shehecheyanu for seeing him? [Rather, they showed that he is very dear to them.]

Note: Perhaps their Chidush was that one makes both Berachos. Mishnah Berurah (1, above) considers this to be a Chidush. This is unlike Mechayeh Mesim, which exempts Shehecheyanu!

Damesek Eliezer: R. Yonah and Tosfos (58b DH ha'Ro'eh) teach that one blesses Shehecheyanu only if he is very dear to him. The Rosh, Tur and Shulchan Aruch say so also about Mechayeh Mesim. What is their source that this depends on Simchah?!