i used trillian pro 3.1 in the good old days…
its nice being able to rename people so you don’t have to remember which screenname belongs to who. also, you can send a message to everyone at once, which is handy. its nice to be able to sign onto all of the different services at the same time, too, but not that useful if none of your friends use them. of course, tabbed browsing is nice too. but now that i have linux, i use gaim (also available for windows), and don’t miss trillian too much.