I have recently become a big fan of the D1H after having owned a D1X, D2H, D50, D70, and D200, although I'm still learning its capabilities. I bought it to complement my D200 with the hopes it would help better capture my toddler running around in available light situations.
From what I've read, and as others have already noted, the D1 had some user interface issues within the menus and firmware quirks (sorry, I can't be more specific).
For my purposes, a Dad trying to capture my little girls growing up, the D1h has been a joy to use. Its defintely a pro-body, as fast as my D200 in terms of FPS, focuses faster than my D200 in normal and low-light situations, has less noise at high ISO (although not in the shadows), picture reviews are quick to display (although its 2" LCD shows its obsolescence), and it has a 40 jpeg (and I believe 27 RAW) buffer. All in all, it adds up to a nice camera for photojouralism, which is what many pros have used (or are still using) it for.
Sure, its only 2.7 MPs, but for my preferred photojournalist/candid style, and the fact that I never go larger than 8x10, it fits the bill. Plus, I don't dread the time when I have to post process those files. My D200 RAW files are painfully slow to process and convert. I believe the D1H's "fine" jpeg mode is about the same resolution (about 2000 X 1300) as the D200 set to Normal size, and "medium" quality.
At around $400-$500 used, the D1H has been a fun camera to add to my bag.
