I have two on my shop: one is an 8x8 and the other is an 11x10 or so. I like them and don't seem to have the problems others have outlined. I have about 1-2 inches of clearance between the bottom of the big door and the gravel below. Never had anything get jammed or stuck in 6 years. The drafty argument is valid -- I live in an area where the temps are mild so it's not a problem for me. The locking mechanisms I use are catches with lever cams and you'd have to destroy the door to get in. That said, you cannot unlock them from the outside -- again, not a problem in my application. I like the look better than rollup, kind of takes me back to the 'ole days.' I also found them better with regard to overhead clearance. Makes the inside fully open.
But they're not for everyone.