First off, unbelievable work. Not only does everything look great, the code is equally well thought out.
I just started to play around with some examples from your recent blog post on BasicDialogs. In IE7, I noticed that the top border doesn't show around the tab area.
Oddly enough, it does show up if I bump the height to 2px-- but showing 2px in height. I'm not sure what would necessarily cause that flip of visibility between 1px and 2px.
border-bottom:1px solid #6593cf;