I have a rotary grater and I hate it. It takes twice as much effort to squeeze the #$%!!ing thing shut as it would to just use an old fashioned grater. I wake up with DOMS in my hands the next day.

If you're thinking of getting something more helpful than a regular grater, consider a small food processor. I got a little wee Black and Decker one yesterday for fifteen bucks. It's perfect. The pieces go right in the dishwasher.