My 660 stopped for no apparent reason last night, with about 3 minutes left in the Springsteen show. I had battery power left, and 35 minutes left on the disc. The only explanations are either that I hit something that caused it to stop (I had LOCK on as per usual), or that it shut down because of heat. I guess after running over 2:30 straight inside of a little bag, it was too warm. The deck was quite warm when I pulled it out of the bag. The only other time I had a problem like this was in the rain with Richard Thompson, a problem that I attributed to excessive moisture.
I have to say that it pretty much sucks that I can't depend on this deck to run without fail, and that it will just stop without reason.
Fortunately, I did end up getting 99% of the show, and only lost the last half of the last song.