I did my first concert recording last weekend with my 660, John Mayer. I really like the ease of use. I had a problem with the deck about 10 min into his set( recorded both opening acts without a hitch) it powered down, I thought it was the batteries, but they were new, I took em em out moved them around. I turned it back on and was getting errors, I took the CF card out and blew into (fearing a piece of dust), put the card back in, did this several times. nada. took the batteries in and out again. then again took the CF card in and out several times and then it just worked for no reason. the CF card is sandisk 2gb ultra. have had no problems with it prior or since. after rereading this post again, I think I am going to get a kingston CF card, and make sure my battery connectors are all good. those seems to be the most common issues.
I am looking forward to allmans/ratdog next month =D, gonna take the 660 on the road =D