I too love Trillian very much, it is a great project and I very much admire what Cerulean has done. I love many of the features, especially the logging, which I missed when I switched off of ICQ. The AIM blocking was a real pain in the neck, though, as has been mentioned, although it served as an interesting springboard into something that has been really cool. My roommate and I got sick of AOL and decided that depending on their networks, or anybody else's networks, was more than we wanted to put up with. So we tried to envision a new kind of chat client that had such low server dependency that a server wouldn't even be totally necessary all the time.
Our vision has come true in
BitWise. We have written a server and a client from the ground up, and we've added almost all of the basic functionality that you need to comfortably message, and even some unique features to boot. Including an option where you can "log in" without the server using cached information, and even talk to your buddies if they're online at their last known IP address. This also works great as a "stealth" mode if you want to go almost undetected.
One last comment--because we're writing this thing from the ground up, with our own protocols (not relying on anyone else's), we have much more flexibility. You want something in your chat client? Ask for it, we may be able to do it. If you've always wanted that certain feature, you can let us know and we can put it in with everything else (assuming it's reasonable).
Note I'm not putting down Trillian--just pointing out that it still has dependency on other systems and is limited by that. I still use Trillian myself religiously.