It needs a larger area to write on

I worry that if this design were to be chosen that at any stage in use the mouse will catch on the circular notepad area, either on the tab or the upper layer itself..

This is the least practical design in my opinion.

Question is if people want their mouse to be able to go over their writing. It is very important that the user doesn't accidentally "scratch" the writing area, thus erasing what the user had written.

Like the quirkyness and style, but reverse the scratch-pad area with the mouse-pad area; have the transparency lift off the circle instead of the other way around -- maximize writing area, encourage doodling, and help keep the overall surface cleaner (since dirt and other particles wouldn't be as likely to get stuck in unreachable areas).

This sketch sparked an idea: If that circle area could be moved around the mousing area, that would be really cool. Like a post-it, but peel to erase and then stick anywhere on the pad and scratch...

I like the design, but I'm afraid it will make mouse usage (= primary function) annoying

I would wonder how the scratching surface would attach to the mousepad, because it is a circular area with no "top" to attach.

Good, but it seems like too small of a area.