We've added a tutorial for the Billboard Generator Generator (a tool that lets you project pictures or text on any flat surface). Support for masks has been improved, so it is even easier now to project to non-rectangular surfaces. For example, here's a stop-sign generator:

And here are some boards created recently by users:

Notice JaySticLe's use of masking for the fingers over the piece of paper on this last one.

(Update: fixed broken links to user boards, sorry about that...)