Facebook really is That company. Which company? That one. That company that shows up once in a very long while–the Google of yesterday, the Microsoft of long ago. That company where large numbers of stunningly-brilliant people congregate and feed off each other’s genius. That company that’s doing with 60 engineers what teams of 600 can’t pull off. That company that’s on the cusp of Changing The World, that’s still small enough where each employee has a huge impact on the organization, where you think about working now and again, and where you know you’ll kick yourself in three years if you don’t jump on the bandwagon now, even after someone had told you that it was rolling toward the promised land. That company where everyone seems to be having the time of their life. … I’m serious. I have drunk from the Kool-Aid, and it is delicious.”

– Facebook manager Justin Rosenstein, June 15, 2007

Facebook manager Justin Rosenstein once described the social network as “the Google (GOOG) of yesterday, the Microsoft (MSFT) of long ago.” Today, Rosenstein perhaps views it as the Facebook of So Totally Last Week because he’s leaving the company, along with departing Facebook co-founder Dustin Moskovitz. Together the two hope to develop some sort of new extensible enterprise productivity suite, something that will be “to your work life what Facebook.com is to your social life,” according to a post on Rosenstein’s Facebook page.

“We see this new venture as very complementary to Facebook,” Rosenstein explained. “We hope our products will become to your work life what Facebook.com is to your social life. Our software will use Facebook Connect as the default option for identity and authentication. Our user interface will adopt many of Facebook’s conventions, creating a seamless and familiar experience for current Facebook users. And if our new development tools turn out to be useful, we hope the Facebook engineering team will come to adopt them.”

The departures are a blow to Facebook, which has been suffering something of a brain drain recently, and more specifically, to CEO Mark Zuckerberg who founded the company with Moskovitz while the two were undergraduates at Harvard.

Comments like Moskovitz’s are a far cry from the accusations of talent-hoarding leveled at Google just a few years back. “Google is doing more damage to innovation in the Valley right now than Microsoft ever did,” LinkedIn founder Reid Hoffman told the New York Times in 2005. “It’s largely that they’re hiring up so many talented people, and the fact they’re working on so many different things. It’s harder for start-ups to do interesting stuff right now.”

Quite a contrast in perceptions, yeah? Funny, how quickly the hottest-of-hot Valley companies can begin to lose currency in tech’s talent pool. Not that we haven’t seen this sort of thing before. “Twenty years from now, Google … will essentially become the Microsoft of today,” said management consultant David Goodenough. “This is the norm.”