My last car did not come with luggage racks; the roof was just flat. I use to do a lot of kayaking and had two one man kayaks that I often carted around on the weekends. Since I didn't have a rack to put them on, I bought me a Thule.
Basically what you did was turn the "screws" on each side of the rods to they fit tightly around the door jam. The door just shuts on them. There is rubber on the bottom of the pads that touch the car and I never had any trouble with scratching or chipping of the paint. The whole process to put the racks on or off took about 10 minutes and could be done (and was done) by just one person.
I was very happy with this system and would recommend it for anyone. It's a bit pricey but worth every penny for the ease of use and dependability.