A little thing that could be improved, in my opinion: when, in your settings, you ask to not be seen online by other users, you still see yourself online (= with a green dot) in discussions, or in the userdirectory extension.
It's confusing, because many time, seeing that green dot, you wonder if you've actually activated the "not being seen online" button, and have to go check it back. And this green dot you're the only one to see is unnecessary, as it gives you an useless information (you already know you're online because you're currently visiting the forum - sure, you could visit it disconnected, but then a lot of things change in the display of the forum, and therefore you quickly know it).
To sum up: I think it would be more clear to see yourself (= without the green dot) as other see you. Or at least to show it differently when you made yourself invisible (a pale green dot? an empty green dot? a hatched green dot? a grey dot?).