I use it as well...I guess it's one of those applications everyone uses...it really is a great software after all...can handle almost every messenging protocol out there and on top lets you customize the looks of the application in every way you can imagine.
iChat supports MSN through Jabber, thats how I use it. iChat with MSN
nice little tutorial if youd like to try it out. I have no idea how to add buddies using MSN this way though.