I have one and I love it. I honestly don't think I would have progressed to where I am at, quilting-wise, without it. I always had trouble holding the ruler still and straight when cutting, which lead to a lot of frustration and ruined fabric.
I just picked up a used one from Craigslist for a real bargain. Don't know what I'm going to do with two of them, but I couldn't pass it up!