Yeah, after a while the velcro gives out, and either your saddle bag falls off, or it almost falls off. One time I was riding, and felt something hitting the back of my thighs as I pedaled. Turns out the velcro straps that go over the rails had come undone and it was just hanging by the loop around the seatpost, so it was swinging side to side with each pedal stroke.

I still use that saddlebag, but I cinch it up to the bottom of the saddle with an old toe strap.