Yep, me too.
From my limited testing, if I quit and restart Adium, the event sounds will work for a while. It seems that if I sleep the MBP and then wake, the sounds no longer work.
I've gone into the preferences and re-set the sound package (I like the duck sounds 😉 ) and that doesn't help. Only a quit and re-start will help.
All other sounds work normally during this time -- Quicktime, Flash movies, OS sounds, etc. It's just Adium that's broken.
I even tried the beta release and got the same problems.
Mike