Y Combinator, the increasingly famous Silicon Valley incubator, announced two new general partners today — Gmail creator/FriendFeed co-founder Paul Buchheit and Harj Taggar, who was already working at YC as a startup advisor.

Buchheit (who has been making angel investments on his own) joined Facebook in August 2009 when the social network acquired his previous company FriendFeed. The YC blog post announcing the new partners implies but doesn’t explicitly say that Buchheit is joining the incubator full-time. He confirmed via email that he’s leaving Facebook. Today is his last day.

The news may seem like a blow for Facebook, since Buchheit was a nice coup in the talent war between Facebook and Google. (Facebook chief executive Mark Zuckerberg has said that the company’s acquisitions are all about hiring talent, not acquiring technology.) Plus, the announcement comes right before Facebook will probably unveil its own “Gmail-killer” on Monday.

(Update: Buchheit commented about his departure on FriendFeed, where he said, “It has less to do with Facebook and more to do with me. I’m just more excited about helping new entrepreneurs create the next Facebook or Google.”)

Still, Facebook hasn’t done too badly in the deal, since FriendFeed co-founder Bret Taylor is now Facebook’s chief technology officer (and he’s been much more public in his role at Facebook than Buchheit has).

It will also be interesting to see whether this changes the dynamic at Y Combinator. With a number of partners, YC is hardly a one-man show, but sometimes it can seem that way — Paul Graham is definitely the incubator’s public face. With the addition of Buchheit, YC now has a second partner who’s pretty famous and respected in the tech world.

Front photo via notphilatall on Flickr