tunes
I was just checking out the new Microsoft Music site which is supposed to compete with iTunes. Looks like they have a decent selection and it is nice to be able to use WMA since that works on a bunch of different devices. But, it doesn't have anything that will pull iTunes users away - same prices, same idea.
I do like MSN Radio, which I've been a subscriber to for a while now. Decent stations and it works anywhere you have connectivity (which is darn near everywhere I spend anytime). I don't see much significant in the upgrade though - if you liked it before, you will still like it. If not, then it probably won't change your mind.