ICQ on the Mac was never top-notch. Way back when, it was a questionable, buggy, hobbled Carbon application under OS9 and X. You couldn't do much with it: file transfers worked maybe twice, ever, and doing anything but the most simple of things was nigh unto impossible.
Then it went away for a bit. The developers actually said that they had no intention of making an updated Mac client. But it came back -- under new ownership, I'm given to believing -- and came out with... this.
This is not like the old, crusty Carbon ICQ. This is less an application and more like something you'd put ointment on. It's wonky, it works sometimes, there's just something about it that smells a little... off.
If talking to the three or four people that still use ICQ is really, really, really important to you, then by all means, have at it. But if you're not... there're are way better ways of communicating.
Like the postal service. Or smoke signals.