Anderson Silva is a typical example of a guy who comes over from Pride (where he didn't do so hot) and dominates the mediocre fighters of the UFC.
You hear that a lot, but UFC fighters going to Pride have a much better record than Pride fighters coming to the UFC (which, I'm pretty sure, is actually sub .500). I wish I could find the actual numbers, but I was actually very surprised, all things considered, because I had always thought Pride was a different calibur, and to see that maybe its not as bad as people seem to think.

EDIT: To clarify...."I wish I could find the actual numbers" means I saw a breakdown of it once, but can't find it at the moment, not that I'm making this up, and the numbers may or may not back me up