I used the Meguires Clay bar kit, right before I went to Roswell.
I LOVED the results however, WHOOO! It was a TON of work AND it took FOR-EVAR! If you do it the right way... per the directions, You a are only supposed to do a VERY small area at a time. We are talking like a 12 x 12 inch square area at a time.
That said, it took me around 3 hours to do it.
The results were well worth it though. AND I would recommend this kit to anyone. But Oh man, your will be pooooped when you are all done.
My car looked like glass. Seriously, I have a platinum grey car, and I have never seen my reflection in it before, like I did with this kit.
Thumbs up too!