I recently set up my own Q&A site, and also created my own theme (ClearCobalt), since basically all of the themes I looked at were way too ... colorful for my taste.
The goal was to have a more StackOverflow-like look as well as match the style of my blog.
If anyone is interested: https://github.com/ansgarwiechers/q2a-clearcobalt
Version 1.2 adds stylesheet generation via Less.
Version 1.3 adds a mobile-friendly view.