There is also the bondo-glass product - it has fibre glass hairs in it and I am giving that a try on one ugly bit. I have a bud who used it on a step fender on a 17ft box truck - sees a lot of traffic and still is ok after 4 years. I would use that on a thicker repair, or one with a hole, but agree with the rest that over 1/4 " means hammer and dolly time.
