Update: I have reached 950 hours now, and the Predator sounds awesome. My unit has definitely improved, and dramatically so, from the day I got it a couple of months ago.
Last night, I plugged the Predator into my "home system"... Apple Lossless via iTunes to USB, and Sennheiser HD600's. I've been building a separate iTunes library of ALAC files, instead of the AAC 256VBR files that I use on my portable rig, and I decided to try out a few of my favorites. Maybe it was the wine, but I truly enjoyed the session.
I have never been completely thrilled with the sound of my HD600's from the portable. However, using the Predator's DAC instead of the iPod's, and the lossless files instead of the compressed, makes a significant difference. The bass is deeper and more refined, and the soundstage is expanded. It may not be a substitute for a home system, but you could do much worse than the Predator if you are on the road with your laptop and a set of full-size cans.
I have decided to go on to 1200 hours because it isn't costing me anything except a bit of electricity. Surely, that will be enough!