Hey all,
I know this is probably something that could be suggested to the admins, but I went ahead and wrote a GreaseMonkey script to take care of it for me. The forums seem to be locked into a 955 pixel width, and I have an OCD about using available space efficiently in my browser.

The script just goes through and resizes the width to 100% to make the forums and threads use the full width of whatever size your browser window is.
If anyone wants to try it out, heres the link:
GreenPassion Modifier
And if you're not familiar with GreaseMonkey, its a Firefox addon that allows you to change how a website is displayed in Firefox.
Homepage FF Addon page
-D