Shiny surfaces such as backs of iPods: use the Cermark laser etching spray - we get ours from Laserbits. Spray the back of the iPod, wait 15-20 minutes then etch as usual. The power should be 100% and the speed should be the wattage of your laser, for us the speed is 35 since we have a 35W laser.
After the etch you just rub it off with a damp paper towel.
I've used the Cermark tape for people that are nervous about having their equipment sprayed and it works quite well. I've also purchased the paint on and it's much more economical and easy to apply. I've been using the LMM6000 purchased directly from Thermark. Buying at least the 250 from Thermark directly is about the same price but the 500 is cheaper from Laserbits. As with a lot of things, the more you buy the better price you get. [Aaron Haley]