Nice layout. Not sure about some of the colours in certain areas but overall it's a nice clean style.
Just a suggestion. It wouldn't be a bad thing if you changed the subforum icons and button set. Re-coloured stock vbulletin buttons don't suit this style at all. Go with something custom that compliments the theme of the site. It will look far better from a visual perspective.
Dunno if you noticed (maybe you did) but there's a couple of sets of toadstool emoticons i designed that you may want to use on your forum. You can locate them in the vbulletin.org
Database.
Overall it's a nice style. Nice work.