To sharpen the blades you backlap them. Basically you put some type of compound (I bought valve grinding compound at the autopart store) on the blades and spin them backwards. You can order a sharpening kit or you can DIY something to spin the blades with a drill or some other machine so you don't have to turn a handle yourself. It does take time, but from what I have gathered its the best way to do it.

Fizzaly that lawnmower cracks me up. Nice work. =)