So as you can see, my new theme is live. I still consider it a work in progress though, so don't be surprised if it changes.
Having now played with BlogEngine.NET themes, I can really say that I'm impressed with the theme mechanism and layout. Modifying an existing theme (CoffeeCup by Michael Silvers) was an absolute breeze. There are no tables in sight, the CSS crowd will be pleased. A nice side effect of using standard compliant HTML is that the blog is viewable even from a text browser on Linux like Lynx.
I know I will be using the BlogEngine.NET layout as a template for any new sites I design. Just another way that OSS helps to educate the masses.