I never ever used Messenger and had to go to some lengths to stop it automatically starting each time the PC was switched on.
I suppose it was because I never knew anyone else who used it - perhaps I was too old for it? I came across a few people who had the interface load each time with a username but I never asked them what they used it for.
I've got Skype but hardly ever use it as I've got a phone with free calls which came with my broadband deal. Other than that, I'm on Facebook daily but not Twitter.
I would guess Facebook & Twitter have probably been the final nails in the coffin.
I have used MSN Messenger and WL Messenger since the day it came out and it has been a great service. I often chat with friends and family from all over the world and we see each other so it is almost like having them in the same room. Skype used to have a huge energy demand so I never went down that route but since Microsoft has bought it I fully expect the new Service whatever it will be called will have the best of both worlds. The new Microsoft replacement for Hotmail, Outlook is so much better and easier to use and has done away with adverts. All you have to do is remember what it used to cost you to make an overseas verbal call and then see that you get the same free but with live picture feed at the same time so to me it is really a no brainer to use the service.