Well for there intended purpose of Instant chat in otherwords paging someone and telling them to meet you on irc or in a game etc...I find AIM and Messenger much more pleasant. I find alot of people orginally made ICQ accounts because there was no other alternative then AIM became avaialable to everyone and they started switching to it but it was promptly shutdown due to some illegal usage by microsoft and others at which point most went back to ICQ and hence the rest of the community in its attempt to be 3L337 sets up ICQ accounts.
The whole leet thing aside though AIM and Messenger both allow you to use NAMES not some st00pid number that you can never remember which makes them far superior in my book.
The only time I ever use the program is to page someone and tell them to meet me somewhere.
ICQ Whats your number? Hold on lemme go cut and paste it LOL
AIM and Messenger whats your 'number' Boogieman OK!
ICQ SU><0Rz its for the folks attempting to jump on the 'leet' bandwagon when most of the 'leet' has already left

Hehe Sorry if I offend anyone thats just my take on it.