I have a messenger for each of my friends. I use almost all of 'em, I'm fickle when it comes to messengers. I started out using AIM only, then switched to Yahoo, then to MSN, then I got ICQ. I have at least one person I talk to on each messenger - except more of my friends use MSN - so I use 'em all.
You can play games on YIM as well... I prefer chess.
Yeah, I use it because some of my friends are on icq and some are on msn messenger and so on... This way I wont have so use several programs just to chat with them.