We have a Performance Bike brand roof rack for our Honda Accord. We take it on and off every time. It only takes maybe 5 minutes to get it on and off.

We've never had a problem with the bikes coming off, or loose, or anything. And its never scratched the paint on the car. The one thing I will say, if your bike is exceptionally heavy, or you are too short, I could see it being a problem. At 6'1", I don't have much problem lifting my bike up to set it in the tracks.

Oh, one thing about a roof rack, don't mount your bikes on it until AFTER you back out of the garage.