I asked the same question in the DR-680 thread, but I'll ask here too as I'm interested in both and the last Tascam deck I used was a cassette portastudio in the late 80's:
What happens with an intermittant power blip? With my Edirol recorders, at worst the recorder's settings remain intact, I can resume recording to the same card, the file can be simply transfered off card later with the good files and I just need to rewrite a new file header.. the occurance may be rare, but shit happens, and less than graceful performance when an unexpected power blip occurs would be a big step back in reliability and potential agravation IMO.