Auto Closing threads . . . Eh, why bother?
A web site to Accompany Cforums.org . . . Too much work and not needed.
Formatting in sig's . . . I pretty much disable sigs. They are mostly annoying. Besides, if we can't have custom avatars, what makes you think they'll allow this?
300 second wait time for PMs? . . . Stupid idea. I've never had problems at more popular forums with PMs.
Trade rep . . . Nice idea, I've seen it elsewhere. But as said before, not enough deals are done here.
Review section . . . Only good idea that would be useful to the site.