I talk to the most people on MSN (all folks from here of course), but I'm on AIM all the time just in case someone from RL wants to contact me (which happens occasionally). I'm always away on AIM though, even though I'm very often NOT away. Sometimes my away message is a conversation-starter (I NEVER use "I am away from my computer right now" as an away message, and I despise it), often it tells what I'm doing, and it's a chance for me to be witty and creative. I don't put up an away message; I craft one. Also it's one of the main ways my parents gain information about my life. Yes, they use AIM.

I also like MSN because it's where I talk to a number of people from EoFF, plus all the reasons Greed-ness mentioned.

Yahoo is just terrible in comparison.