After upgrading to 0.81, I've had a few issues with people not seeing that I'm online on MSN. I appear as offline, but I can still talk to them if I try to send them a message.
It only happens to a few people, and they're both users of Adium and the official MSN-client. It's also happened using various network set-ups and routers (belkin router, netgear router, internet sharing via a powerbook), so I doubt it's some problem with ports or anything like that, although I'm not ruling it out completely.
I'm not aware of any specific circumstance that will allow you to reproduce the issue, since it seems quite random. I'm hoping more people will report better on this issue. Sorry I can't be of any major help.
