I don't understand why so many people think of a "me-too" a bad thing. This way we would have only one automobile brand, only one clothing brand and the list goes on...
The me-toos that CAN succeed is the one that actually do it better -- they can implement an existing concept in a way that executes better or, in the case of a web service, engages users more effectively.
I just submitted an article from OnStartups.com that talks about this in a little more depth. Maybe this will spur some more good conversation:
See http://news.ycombinator.com/comments?id=754
I will just aggree that if you can do it better then just do it.