OK, I guess I will be the first A$$ in this thread. Every time I see the thread I want so bad to type something but I have resisted. But now that it is on its way to 3 pages....
I am not doubting anyone's bags have come off and slid down the highway. I am doubting, however, that this is a mechanical failure of any kind (post-'08 latch recall). I will always say operator error. My bags ('09) are by no means tight fitting and move around considerably if I grab hold and lift or try to move them. It is VERY EASY to not put them back on correctly. You might miss putting the bag into the front bracket or one of the 2 slots. Heck, you might put the bag on the wrong side of the bike (yes, they WILL fit on the opposite side!). I am so paranoid about putting them on wrong, I ALWAYS grab and lift to make sure I put them on solidly. I sometimes have forgotten to double check before I depart, I will get off at the neighborhood stop sign and check it again.
Back in October of last year, the bike had roughly 20,000 miles, I had a run-in with a minivan who decided at the last minute he wanted to be in the turn lane I was about to occupy. Trying to avoid him, down I went on the left side at about 15-20 mph. The bike slid over 125' and had major damage to the mirror (basically broke it off at the frame mounts), bag (bent the mounting bracket behind the plastic) and foot controls (snapped the shifter off). However, the bag stayed on the bike, did not open and took the brunt of the impact saving a lot of plastic on the rest of the bike. (BTW, I GOT A TICKET FOR FAILURE TO CONTROL A VEHICLE!!!!) Funny thing is, I bought the bag brackets from ZSteve last summer, but never put them on.