There’s a decent article/interview with Charles River Ventures representative Susan Wu over on the Worlds In Motion website (Link). Here are a few excerpts:

“The distinction between what Facebook and an MMO looks like is going to disappear,” Wu says. “All social interaction online will be driven by game mechanics.
…
There are all these Web 2.0 conferences, and Web entrepreneurs basically talking amongst themselves in this insular environment, and I see the same thing in the gaming industry, which has always been a cottage industry and very segregated. I see so many different parallels going on in these two communities
…
“One of the hallmarks of a successful Web company is — if you look at the track record of the most successful companies that have stayed independent and sustainable, like eBay, Google or Amazon — they have built platforms [which can] foster entrepreneurs. There are ecosystems that spawn innovation from the community members themselves, and Facebook is falling in with that too, with the new platform launch.

I’ll just say that I see other parallels; most notably in the serious games arena and Product Lifecycle Management applications.

Also, while I agree Facebook has created its own (walled garden) ecosystem which is helping to spawn new applications/widgets (much as MySpace did), I don’t equate Facebook with eBay, Google or Amazon. Those companies still serve pretty much the same audience to whom they originally were targeted. Facebook doesn’t. I consider that a rather big deal considering what Facebook provides.