I like the vBulletin better then what was being used before. It sort of bugged me when you went into a topic and the nested path got longer and screwed up the page formatting.

The only real problem I see is little stuff like the colors. They are pretty high contract and if there is red or yellow, or even blue, they can be very difficult to read. Even the white text can be a bit hard on the eyes. I agree with others that the active/inactive thread indicator is also difficult to read. Maybe choose a lighter red or lighten up the background. The background image probably isn't helping since it's striped and forces the eyes to adjust to the pattern.

So what am I saying, less contrast between the extremes in colors would help.