I think it depends on who your circle of friends are, most of mine use Skype, I had an MSN ID, but haven't logged into it in a year or two so it's probably gone. Skype just transitions from chat program to phone dialler so smoothly it's hard to stop using it.
Well, this does seem a little bit of an odd move, considering that (in Ireland anyway) MSN seems to be king of the hill as regards messenging. I guess it's different elsewhere but everyone I come across locally uses MSN, yet most don't have Skype installed. Maybe they just want to merge the two into one massive worldwide messenger network? Seamlessly using MSN and Skype in the one application is somewhat appealing...