I have AIM though I rarely ever use it. It's an ok service if a little barebones.
I had ICQ, but I long ago abandoned it.
Technically MSN/WLM is discontinued... But you can still access the servers if you use third party software. (So programs like Trillian or Pidgin can still allow you to sign in and send messages over MSN without demanding you upgrade. Though I had heard this ability was only going to be around for another year before it gets removed.)
Personally, I'm not really comfortable with this move to Skype... I don't like the idea of P2P connections used to transmit my data. (Nor the idea that my internet connection is used to transmit someone else's data. Especially since I really don't have a good enough internet connection to be sharing like that. My upload speed is pretty limited and it wouldn't take much for P2P connections to completely hog every bit of my upload speed and slow my internet to a crawl. And couple that with multiple other people on the same internet connection is just a recipe for problems.)
Yes, the name Skype actually comes from (and was originally going to be) SKY PEer to Peer.
Which is why if you're using it, you may find that your net is slower. (Since it takes user's bandwidth to help transmit IMs, calls and in some cases video around.) And if you have bandwidth caps, you may find that you're closer to your limit if you leave skype open any amount of time. (Since skype keeps using your internet even so long as you keep skype open, even if you aren't actively using skype.)