Picked up my z3100 44" today. Tip for the price conscious: see if your local university has a campus computer or tech store that will order in from HP. These folks aren't really in business to make money from computer products, so you can often get a good price, especially in smaller market countries where there isn't much competition. I'm in Canada and saved $500cdn over the lowest fly-by-night internet company i never heard of, and thousands off the price of reputable shops. Disadvantage: they probably won't ship, so you'll need to get it home yourself. I rented a van from the Home Depot ($19 for 90 minutes) and made it just in time.
My studio is in my attic. We had to unbox it on the ground floor and take all the pieces upstairs; the printer body itself was very difficult but my wife and I managed without damaging either bodies or devices.
No prints yet -- took most of the day to get everything assembled and installed, etc.
1) Initial problems with loading the matte black cured themselves after a head cleaning.
2) You can't, as has been mentioned, install the drivers without the printer being ready.
3) It would be really nice if the 3" strip that gets trimmed off the front of rolls was optional.
4) Does the thing ever get completely silent? I don't like noisy devices. I think sleep mode ought to actually sleep!
Will continue to report as things progress.