Brian,
I did some consulting for Car-Top-Tent. They shipped me one of their first Discovery units, which arrived from China in August of 2005.
I mounted it on the Trooper and Tacoma and used it on several trails in AZ and spent a night in it in Sedona.
When it matters, the unit is actually pretty good (bow structure, pad, etc.); however, it is a "fair" weather roof tent. The material is regular tent material and the rain fly provides minimal coverage. The ladder design is also marginal, and actually takes longer to set up than the tent itself. The tent cover is the biggest downside. It is not waterproof and is single stitched in the corners. But, the tent does have good bones, and wont fall apart on you.
Just know, it is a fair weather solution only.