I think they new interface isn't the "online contacts" sidebar anymore, they've got a separate HUD view for that now (sidebar -> small icon next to "CONTACTS"). If you use that for starting conversations and hide the main window, it's actually somewhat usable. Would be better if there were an option to hide the silly avatar pictures there, too.

Edit: Just noticed that the HUD window is always on top. Dang. Let's see if that Adium plugin is still in development…