Speaking from my personal experiences with Skype and Windows Live, I would actually like this change quite a bit. I use Skype as an instant messaging tool more than I use it as a voice communication tool, and I like Skype's neatness and general presentation a lot more than MSN. The only thing that's mildly lacking is perhaps the ability to see your own avatar in a 1-on-1 conversation, but the ease of quotation and cross-reference as well as the program's 1-window-has-everything interface has essentially made me pretty much abandon MSN altogether (and ask my friends to sign up for Skype instead).
As for Skype's new message notification sound ... MSN's is much more annoying and the pop-up chat window is many times more obtrusive. Though, you can turn it off in either case.