Will the real Bill Clinton please stand up?

For a while, I was being followed around by Bill Clinton. Quite flattering really. It came about because I followed him on Twitter, and his account must be set up to follow all followers (still with me?). All fine and dandy so far. However, today there was a very rude "tweet" about Obama and I thought "oops". Clearly it was an impostor, or Bill has completely lost it (obviously the former). Anyway, I've stopped following him. However the Barack Obama twitter account that I'm following seems to be genuine.

It's really hard to tell what is real and what is not on the Web. On facebook, I'm "friends" with Russell Grant and Jeremy Clarkson. I think at least one of them is real (or at least it's created by their PR person with their approval). Personally, I can't be bothered to impersonate anyone, since it's tough enough to keep up with social networks as me. I wonder how many Slim Shadys are online?