Is it? How temporary? We know that Sirius is aware enough of the fact to comment on it, but can we prove that his mind hasn't been altered? Look at Peter - he's described, even in human form, as being ratlike in his behaviour. Is this because he was already ratlike when he became an animagus, or did his long stay as a rat alter his behaviour? Or is it a combination - he was already ratlike, but it's been exaggerated by his time as a rat.

This applies to people who change into forms that suit them, of course. What about people who change into forms that *don't* suit him - would that alter them in a way that we can see?