So I've finally seen a badly scratched BD disk, a Netflix rental. It had a deep groove about an inch long and running almost parallel to the edge, and a bunch of smaller damages along a straight line, probably from those mail processing machines. I had thought there was no way this thing can play considering what I'd heard here previously.

To my surprise, the movie played without a hitch. Was it error correction, was the damage contained to foreign tracks or previews or extras (not too many on this one and unlikely from the size and spread of the damage), or what? This was on the LG dual-format computer drive.

Also, is it possible that some disks are manufactured without the hard coating (this was a Sony release)?

http://www.youtube.com/watch?v=o5jEbZt6AIQ :)

Also, is it possible that some disks are manufactured without the hard coating (this was a Sony release)?

No. All Blu-ray discs feature the hard coating.

Movies are put on the DVDs from the inside out. So if the disc has scratches close to the outside edge, it will less likely cause you problems, as there might not be anything there to begin with.

With Blu-ray the data layer is .1 mm deep. as long as the scratch is less than .1 mm you are OK. SD DVD, CDs and poor old HD DVD the data layer is .6 mm deep. With those you can actually buff out any scratches that are less tha about .4 mm deep.