Y Combinator, the seed investing and startup incubating powerhouse, announced this morning that it has added its first two new investment partners since launching five years ago.

They are: Paul Buchheit, creator of Gmail, the prototype for Adsense and the Google slogan "don't be evil" and Harj Taggar, a Y Combinator employee who previously built and sold an eBay auction automation software company. Buchheit will reportedly leave Facebook to join the incubator. Y Combinator helps build small startups, runs the widely-appreciated Startup School and owns the startup-focused social news site Hacker News, among other projects.

Y Combinator founding partner Paul Graham was short and to the point in his announcement this morning, writing simply that the organization was "delighted" to add Buchheit and Taggar. In addition to Graham, the new additions to the partner roster will join bot-guy Trevor Blackwell, author Jessica Livingston and MIT prof Robert Morris.

Liz Gannes wrote an in-depth profile of Y Combinator this Summer at Gigaom. The organization has experienced remarkable success with startups and exercises significant influence over the startup ecosystem. It's a model for many other seed investment organizations, but its strongest competition for mindshare is Colorado-based TechStars.

Buchheit Leaving Facebook

The LA Times says Buchheit's joining Y Combinator means he's leaving Facebook today, as well. That's interesting, because the man made wealthy by his work at Google said this Fall that he believed Facebook has the potential to be worth more than Google. Buchheit has been at Facebook since his startup FriendFeed was acquired by the giant social network. FriendFeed co-founder Bret Taylor has since become Facebook's Chief Technology Officer.

There's a saying that says some people like to help make big companies great and others prefer to help make great companies big. Joining Y Combinator may be Buchheit's best opportunity for the latter.