Maybe it's a setting I'm missing, maybe it's a bug; but a feature I absolutely loved about prior versions of (libgaim) Adium worked like so:
(In a specfic tab or message window)
JoeSchmoe: I'm leaving now
Me: ok JoeSchmoe is away
Away Message: "I am away from my computer"
Where the away message they set would be displayed in gray, like how the message history works. I was testing Adium .80 last night, and it worked properly for some contacts, but not for others. Although their away message was not written to the message window, the tooltip for that contact did display their current away message.
I was having a similar problem due to an issue with the message stlye I was using. What style are you running and does changing it alter the behavior in any way?
I'm not sure what the definitive list is, but if you test it out with any of the packaged message styles you should be able to tell whether it's a style issue or an Adium issue.