The only problem I have is differentiating between a post and he signature underneath. The faint line separating them is a little too faint. Or there needs to be some background behind the post or the signature which makes it obvious they are separate.
Otherwise I like the style a lot.
The fact that it is mostly colours and fading opaque PNGs, plus most of the buttons being CSS means it's a doddle to change the colours of your forum in the admincp.