I've been using a Wacom tablet since 1995, never in that time I even considered an alternative. But based on this review by Ray Frenden and given the price ($50 versus $400), I might have to think twice during my next purchase.
After spending a week with the 6.25“x10” Monoprice, my Yiynova and Cintiq remain unplugged and I gave my Intuos away to a friend. The Monoprice tracks subtle pressure variances and small movements with less lag and more crisp fidelity than any of the others. It is, put crudely, fucking awesome, in both OSX Lion and Windows 7 x64.
Note that unlike the Wacom, the Monoprice pen requires a AAA battery. Given how many of us are using wireless mice, I don't think this is an impediment.