I just happened upon a decently polished little game called Bricks Knock Off (English translation here) that's actually using the 2.1 branch of pybox2d. Cool!
As you might have guessed, it's a game about bricks. Shooting them off some platform to get a decent enough score to continue to the next level. It features music, sound effects, a few levels, and even a scrolling background.
I only have one comment from the pybox2d-end of things, and it's that the position/velocity iterations need to be tweaked to get the bricks to stack stably. If you check it out, change main.py around line 115ish to be something like:
vel_iters, pos_iters = 15,15