It's not that the idea of redoing the UI is a bad one, but the execution reminds me too much of Skype. Skype went from a compact, easy-to-set-aside layout to an elephant on the desktop. It's ridiculously huge now (size-wise).
Can't agree enough. When I'm using Skype I almost have to stop everything else I'm doing thanks to it's massive window taking up a whole corner of my screen and constantly having to hide/unhide the messages pane.
Adium is fine as is, you can customise the hell out of it, it's tab implementation is solid. The only places it's lacking are more server issues, file transfer hasn't worked in years for me.
