I wrote a couple of Quicksilver plugins to support setting away and back on all accounts on Adium 1.2+.
Just unpack the zip and copy the applescript files to “~/Library/Application Support/Quicksilver/Actions”, you might have to create the “Actions” folder.
Restart Quicksilver and you’re done, just type “Adium set away” or “Adium Back from Away” in QS to use them :)
Any request/bug leave me a comment on the entry on my blog
and i'll try to solve it.