AIM and MSN fanboys are almost as bad as console ones. I use both MSN and AIM. As for people renaming their names on MSN, whoever does that is childish and stupid. You can take that option away from them by naming them whatever you like. I do like how it plugs into itunes and such and can display what you are playing, and the drawing feature is always nice. Instantly turning a window into a multiple contact chat is very good as well.
For AIM the best thing is has going is direct connection, since MSN's send feature tends to have issues with certain file extensions and countries. I mostly use AIM for a few contacts that are still on it, but the majority of my time is spent on MSN talking to my European friends and the few USA ones I've converted.