I picked up Fine Cooking magazine the other day, just out of curiousity. In their Test Kitchen section, they have the above referenced article. The picture will show you exactly what the process is. Basically you turn the rasp-style grater upside down and run it over the citrus. I just used it for a couple of lemons and, boy, does it make a difference. As they state, you can see where you've already grated but most importantly for me is that the zest is contained on the grater and it goes straight into the dish. A winner.
BTW, I'm not sure if this is the "board" where this belongs but I'm sure that will get remedied :)