There are a couple items I am not sure about. First, is the gradient background. It seems a little bright, but I guess it is ok once you get used to it.
Second are the borders around the forums & categories. The side borders are orange, while the top & bottom borders are black. I could see if you used images and use a gradient border, but the black on the top & bottom with the orange on the sides just seems out of place to me.
The third item I checked in both Safari 2.0.4 and Firefox 1.5.0.7 and had the same bad result. If you look at the topic view inside of a forum you will notice the Sort By, etc, drop-down menus. The height on that row is too small in both Firefox and Safari. Here is a screenshot of what I am talking about in Firefox.
So as you can see you should increase the height of the table footer in that area. The same thing happens on the member list page as well. So it seems to happen with all your table footers with the drop-downs in them.
Overall though I like the images and the color scheme and it seems to work for me. So outside of those minor bugs it looks great.