I'd tried Adium before, looking for a usable multi-protocol chat client so I could talk to my contacts on AIM/.Mac as well as ICQ, MSN, Yahoo!, Google Talk. I only have one or two contacts on each non-AIM protocol, so don't want to be running separate apps for each. Adium was cool, but quirky, and it never "clicked" for me. It was annoying, with the silly duck icon, quacking alerts, etc. so I reverted to iChat (after trying Fire again - I swore by Fire before iChat was released).
But, the latest build of Adium frankly kicks all kinds of IM-client ass. It's easy to turn off the cheesy sounds (I've got my copy sounding like iChat), and provides a sweet tabbed interface to view chats, and a great contacts manager. Encryption support is built in (iChat requires a .Mac account for encryption) so that's cool. Not that I send many trade secrets over IM, but it's good to know it's there when I pull out the tinfoil hat...
I tried it out briefly last night with Josh, and it worked great. It's supposed to handle file transfers just fine (Fire borks on those), so the only thing I'll be missing is the audio- and videoconferencing ability of iChat. And, if I need that, it's pretty easy to do a command-Q option-space IC to quickly switch IM clients...