I tried to turn on Direct2D in my Windows 7 VM in VMware Fusion, and after turning it on, nothing is drawn inside the application window. The taskbar previews actually show the contents of the window, though. I tired it both using the Aero and Classic themes.
So, I just realized that I might have been on 3.6b5! :-) Jeff told me that there's a bug about this fixed in 3.6, and Joe knows its number. This can probably be duped against that one.