Yes, but Facebook is fungible. In the same way that MySpace and Orkut were. The only thing that's holding people on your website is other people and a bunch of dumb games. You can say whatever you want about Google, but there is not a single search engine today that is as good in all cases. That's why I'll bet my money that 10 years from now Google will be well and going strong, whereas I have no idea what will happen to Facebook.