There's at least two. One is called Monster Galaxy by Gaia Online which launched in December (http://www.facebook.com/apps/application.php?id=129748227041...). There's another, the name of which I don't remember, that did a ton of Facebook advertising in the last 12 months.
Miscrits.
Does it matter? Hasbro didn't think so when Scrabulous became one of the top games on Facebook.
Nintendo protects the Pokemon brand very aggressively.
That was a pretty specific issue, with 2 complaints. One was the name, and the other was that the board layout was identical (location of bonus squares, etc). It relaunched very quickly as Lexulous with a different board. Damage done, but it wasn't an instant kill or anything.