Great control, I've just implemented it for my application, and it looks/works very well done.
However, I've discovered a small bug, and here's how to reproduce it:
* Start application, wait for it to come up
* Press Left Windows Key + D. This minimizes all windows and shows desktop
* Click on the application in the task bar to bring it back (restore)
* Hover over the title bar, the standard WinXP Minimize/Maximize/Close buttons will be drawn over the custom ones in the upper right corner.
I'm not sure if it's a Windows XP thing.
The Microsoft's WPF ribbon didn't seem to have this issue.