Open ended belt drive for cnc router?

I'm gathering parts to build a CNC router (say 5'x3') and was looking
at McMaster-Carr for rack and pinion info and happened across this
image (uploaded image to the files folder beltdrive.gif) and was
wondering if anyone had ever used (seen/worked with/your favorite verb
here) this type of system. I'm looking for possible alternatives to
ballscrews since I'll be cutting mostly wood and keeping the screws
clean can be a problem. I'm thinking of using two belts on the on the
x, one on the y, and a screw on the z axis. Any info would be greatly
appreciated.

Regards,
Mike