I think your header looks a bit odd the way it doesn't fill out the whole area top and bottom (ie you can see the background colour above and below).
Your main content area from the nav to the footer is a couple of pixels wider than the header and the footer meaning your right frame border isn't as wide as it is at the top and bottom.
I think a thin border on the bottom of your sidebar would be good too.
Maybe a bit more padding top and bottom of your content area.

Yeah, it does that on my other site too. It's because of the border on the background. I'll have to fix that.

There's a tiny border but it's very light. I'll make it a little darker.

And yeah, padding would probably be nice :/

K, I'll make the nav bar changes, and fix the gap in this next update.

Done! It's also up for download. I think you guys should be content with the results!

I also moved it: http://www.biscuitrat.trap17.com/templates/serenity/

Enjoy <3