On my brand new Mountain Lion setup, the Messages app behaves weirdly with remote Adium clients when using a Google Talk account:
- I appear offline in my friends Adium contact list
- These Adium-using friends don't get my messages
- I don't get their messages either
However, it works well with other iChat/Messages clients and Gtalk-in-Gmail clients.
Messages also works well with the same account on my other MacBook running Mountain Lion.
I tried removing the Gtalk account, launching the app while pressing the Option key, recreating the Gtalk account, and aslo using the default options, but nothing seems to work.