I don't know...
I think that there is a lot of overlap in users of the others and they still haven't really gotten the public acknowledgement that napster had...it seems to me that the people using these other services are people that are web savvy enough to find them and figrue out how to use them...
I know serveral people that said they use to use napster and say it sucks that there is now place to download mp3's anymore, until I tell them where to go...
I don't know...I haven't used any of them in quite a while, been too busy, and i already have all the music I want :-)