I think it'd be cool to spice up my PCBs with a lick of spray-paint to the compnent side (before it's populated of course) -but will this cause any problems?  I'm not sure what material  the boards I use are made out of -they're green and translucent- so I'm not sure if paint will even adhere to the stuff.  

Has anyone ever tried painting PCBs with any success?

I paited some boards and didn't have problems. I use the same kind of ink as the ink to draw the traces in the board, but red or blue.

I've painted a couple of boards with no problems. Don't count on it to last forever, but a good quality enamel paint should work well. The boards are made of epoxy and fiberglass so don't expect the paint to stick super well. I didn't keep the boards around long enough to see if they aged well.

Take care,
-Peter