Had a lot of fun with this! A couple of issues:
If you move your mouse super slow toward your pig as your spraying, you can go past your inner circle and have some funky things happen.
if you're holding the mouse down and you move the pig, the camera doesn't follow
I sprayed everything 100% on the last level and it didn't have a victory come up and when I quit it said 100% but still didn't have all the objects listed as clean and when I went back, everything was dirty again
Love the concept, I've wishlisted this, very interesting! Perhaps you should see the percentage of whatever you're currently moused over so you can have a better idea of what's still dirty.