In no way do Pandora and last.fm even come close to solving the "Find me new music I like" question. The databases are incompletely indexed and the algorithms aren't robust enough. As a wise man from another forum once said, "Everyone gets a giant boner over this site the first time they are on it - then they realize its like having a really annoying roommate who owns the stereo."

A mapping site like http://www.liveplasma.com/ would serve you better the more eclectic your taste in music becomes. It's not that much better, but it's more thorough in terms of mapping and indexing, and is a lot more complete than Pandora since it isn't trying to be a radio station.