I got to test this system out (Im part of nvidia's mailing list for certain products) about 2 months ago. Played crisis 2 on my living room pc (i5 750 with a gt240) with no lag just longer than normal load times. Played Witcher 2 as well. While you couldnt change the graphics options too much in either game you got the real game and it played very well.
Im happy to see that nvidia and their partners will be offering this service through facebook because now the facebook people can play actual games (full screen and everything) instead of stupid games like farmville. Casual gaming is the bane of real gamers everywhere and that's whats lead to the disdain for facebook "gamers". Gaikai changes that.
Do you really think people who can't be bothered to alt-tab away from facebook will play any game that takes at least a 30 minute commitment to do anything in? Cloud streaming will hold PC gaming back even more than consoles have already done. Gamers aren't satisfied playing on low settings at 720p and 30fps. And the ones that are haven't experienced the real thing.
This service is more of a "try before you buy", unlike OnLive. I ran a few games on it, including Crysis 2. It's surprisingly smooth to say the least. I'd support this company more than OnLive out of the fact that it provides demos, especially for games that have none.
I don't use facebook nor anything else, just skype, and I rly don't like the idea of cloud gamming, it can be the best server and best connection, still wont respond as if it were in your high-end computer... but I guess this is more for light-players, so maybe thats ok then ;p