iChat doesn't support accounts other than AIM and MobileMe, does it? I haven't really checked the updates on iChat for awhile so it might have been updated since the last time I tried to use it. User experience wise..it doesn't bother me at all, or I can't remember the last time I got annoyed by Adium. Also, the customizable (with a lot of external themes that you can download) layout of the buddy list and the chat windows are quite amazing.
iChat supports Google Chat (natively and also all jabber, too).
How about MSN Messenger and Facebook? (Don't have my mbp with me at the moment to check)