I was going to BYU, and my brother and friend were living in Oregon. We had this great plan to drive to Mexico to go mountain biking. It was going to be an epic trip. My job was to drive myself and my bike from Utah to California to meet up with them before heading on. I had my bike on top of my car (you all know where this is going) and all my gear packed and I was heading out of the parking lot. Just as I was pulling out, I remembered that in the below-ground parking lot, in my apartment storage facility, I had left my sleeping bag. No problem, I slammed it in reverse and headed down the super steep ramp to the underground parking.
The car and rack took most of the force. I think I needed a new saddle and seatpost, and my Marzocchi Atom 80 didn't line up at the drop-outs like it used to--but not enough to stop me from using it. All four doors of the car (an 88 Honda Accord) were pried away from the roof, and the roof was dented on the four corners pretty well. It also did a number to my hood on which the mangled tangle of roof rack and bike landed. I was going way too fast to stop when I hit.
Besides the repair costs, we didn't go on the trip. In fact, we never made that trip. I'd like to say I learned my lesson, but when returning to school after a summer break (driving from Oregon to Utah with the bike on top really jogs the memory of a bike out of your mind) I was excited to see one of the coveted under-the-apartment parking spots open (different complex). Again, as was my driving style back in the day, I pulled in so quickly as to knock my bike right off the rack (same bike) before I realized what happened. I remember being embarrassed more than anything (for the bike, it was old hat), so I quickly scooped up the remains before anyone came out to see what the sound of scraping metal and concrete came from. At this point, my rack was loose enough (see previous accident above) that it really didn't damage my bike too much--mostly the bar-ends and, once again, the fork (which now resides on my wife's cob-web-adorned bike).
I still have a roof rack. I actually put my garage door opener in the back seat when I leave (and on extended trips, I put something in my garage in the way, preventing me from being able to pull in without getting out of my car and moving said item). I won't tell you how many times or how often moving the garage door opener has saved my bike/car.