A thought about the "latest" potion of the sidebar: I'd personally prefer it showing one-two from each category rather than a handful across the boards. So two latest in free, two latest in casual, two latest in advanced - otherwise the slower-posted forums won't be getting much limelight.
(I'd also suggest melding NRP section back into Free/Advanced/Casual and making NRP a tag, but I doubt it is going to happen... Perhaps once we have tag-based filtering/search? Since in all honesty, I've been basically out of the NRP scene ever since it became its own thing, solely because it became its own thing and was no longer by tier.)
I myself am partial to right-align for the sidebar - for a forum such as this, I'd prefer the actual forum-portion to be in the main focus when I visit the page (and left-aligned things tend to be the main focus for humans, at least those using our read-from-left-to-right text, as some research found out), and the sidebar be something I look at secondly when I am not doing something specific. Left-aligned sidebar would be a bit too obtrusive for me for a forum (if we were a Wiki, where'd you'd foremost access things by category/article, then things'd be different; in forum, the subforums are the main "categories" I'm interested in, not the individual RPs).
In regards to Open/Closed tags:
I find Ellri's suggestion is a bit too much division. It'd become clutter.
I'd say stick with:
Closed | Jump in | Applications
(Since "jump in" and "apply" already suggest that the RP is open. ..."Apply (CS)"? "Apply (NS)"? "Apply (sheet)"? Ehh, I assume people probably don't want applicants who don't bother to skim the OP after they see the RP is taking applications...)
Edit:
Horizontal lines are useful for posting multiple characters at once.