Well, I'm apparently the first lucky recipient of a cracked 500M. It looked intact when I unpacked it, but it just made a loud buzz when I plugged it in. I only saw the 1" crack when I looked with a flashlight.
I spoke with Robert at Value Electronics, who was very nice about it, and who put me on a conference call with the shipper. The problem is, though, that the shipper can't or won't take responsibility. The rep first said it was because I had signed for it, but he later said that even if I hadn't, they wouldn't take responsibility. I actually understand their point--it could have been damaged at any point after manufacture, including before it was in their possession.
Again, Robert was nice about it, but I still may have a $2000 paperweight, and it's not clear how much of that I'm going to have to pay. Robert initially said $1000, but he then said he'd ponder it overnight and talk to me tomorrow.
I would think the real responsibility (including providing me with a replacement) would lie with Pioneer, but they're really only admitted a problem with the packaging of the 600M and not the 500M, so Robert didn't think that would pan out.