Why would anyone leave Facebook to join Google's ghost town? Further, Facebook is impossible to successfully clone because part of Facebook's inherent value is that it already has an incredibly large userbase.
You don't have to leave Facebook. And most importantly (and highly likely) you don't need to join the ghost town. You are already there if you are using GMail. Don't you know that after using Buzz?
Why should I, the number of my friends on facebook is tenfold and does not include people that once mailed me about a typo in my blog.