First of all, I really like this theme.
One issue I've noticed on on iPhone 4 (and this may be true for all mobile devices): when you zoom in, the navigation sidebar and content div overlap each other unpleasantly. Also, when you scroll over to the right part of the screen, the content div hides the sidebar.
I guess this has something to do with the position tags? Could you suggest a fix?
Here's a screenshot of this occurring on the demo site: