I'm in a psp group in Yuku. It's not all that bad, but does take some getting use to. The one thing you can't do is make pages. Personally I am waiting to see what Windows Live Groups will be like before I make any kind of decision.
I am watching Community Feedback as well, to find out what would be best. If I can't make pages and such then I am going to be in a bit of trouble as I use MSN groups to make pages and such for a website that I look after for a baseball organization.