@sarahsweets: I actually have one! But I lost it like a year ago. lol.

It is pretty neat. I used to use it for work all the time because my work gave them out for free. (Lots of mathematics and note taking at my job.) In fact, it's probably in my desk at work still, but my drawers/cabinets are messy.

I do think they are worth the investment, though. Maybe I should get another one for myself.