The biggest problems I had with the forums were the text size and when you click on the logo. I thought that the text size was generally too small, and it was hard to read in places (because there isn't very much contrast between the shades of gray).
Regarding the forum logo, it's expected that it will take you back to a home page of some sort when you click on it, yet nothing happens. Sure, there's that tiny little Home button on the nav bar, but it's small and blends in with the rest of the page.
Another knock on the text size when viewing the page in IE: you can't adjust it at all. Luckily for me, I'm a Mozilla user, so I don't suffer from this limitation. However, if I were an IE user, I probably wouldn't stick around the site for long because it's just too hard to read.
