I've had my unit since 2008. Once I read that DSD has a higher dynamic range than 24 bit I started using the highest setting. Storage is cheap these days. 1TB for $100-ish. I generally convert to 24@96 for EQ / editing, but I'm a linux junkie and I haven't gotten audiogate to run in that OS.
I did upgrade the firmware. Scrubbing / whatever while fast forwarding is nice. It do go windows on me when I was playing back an hour concert I recorded. On the second time through, about halfway through it just sort of locked up. Which has me concerned. It was plugged into the wall socket and with batteries in the unit, so it most likely wasn't anything power related. Otherwise no issues(yet).
I've reformatted the harddrive a couple of times, but I have never really had any disk errors to think of. But I'm kind of non-typical in that I mount the drive under linux, copy the files to an NTFS partition (fuse / ntfs3g), then do the proper umount and power down steps on the recorder. Then boot windows and let audiogate rip on the data. Then boot linux again and edit.
Batteries, I just use radio shack specials NiMH 2100mAh. They last about 2 and 1/2 hours with phantom power on. The worst I've gotten is 1 hour 57 minutes with batteries I charged one week earlier and left in the recorder for a week. The best on those batteries was 2 hours 59 minutes with a slight overcharge, the charger stops, you unplug / replug the charger one more time for a few more minutes of charge time. Typically 2 hours 45 minutes-ish till self power down going that route on those batteries. So I trust them for 2 hours, baring that one time I came up a little short. I have some 2400mAh kodak NiMH batteries, but I haven't really given them a run for the money. They don't seem to hold a charge if you store them for any length of time. I just make sure that I charge my batteries within 24 hours of heading out the door. Just to be safe.
My mics are Avenson STO-2's and they don't output as hot of a signal as other mics. 8:30am on the gain knob is the setting where someone could set off a nuke and it wouldn't clip with those mics. I tend to favor large brass ensembles so I'm typically sitting at about 9am if I'm close. 10-11am if I'm far away. At the moment my usage is little more than a glorified camcorder setup. Although I do handle audio externally, until the final render. I tried SM81's, but they were a little hot for the unit (8am). And a bit too directional for a stereo image.
Ultimately I'd like to use MC 910's, or MKH 8020's. I typically record outdoors so OMNI is a bit less problematic in those conditions. I'd also like the try an external preamp since the korgs preamps do tend to be a little quirky with hot signals. And a little light on the low end IMO. But I wouldn't consider myself a typical user.