Good review on the new Z series. I didn't hear too many downsides though...and there certainly are a few.
Paper handling is not very well thought out, and the spindle design is quite dreadful. The end caps are way too small, so if you have a wide diameter roll of paper there is no elegant way to unload the spindle. I understand why they placed the roll on the rear of the printer, but it makes loading paper pretty awkward. You really should leave a good amount of space behind the machine to facilitate paper loading...and learn how to read the LCD panel upside down!
They are also working the kinks out of performance on fine art papers. But the upside...is they are working on it! The engineers have been great, and I've been testing some new media packs, which are showing some improvement (d-max etc).
There are some bugs on the Mac. Michael alluded to one, namely the USB/stalling issue. I've discovered another, which is more annoying. If you apply your profiles in Photoshop (HP or otherwise) and choose Application Managed Colors in the driver, sometimes the driver applies its own conversion anyways. This is highly intermittent, and if it comes out wrong on one print, the next print is usually OK. The engineers say there is a problem with the Mac OS and the driver. I wish they would fix it! Right now for consistency's sake I let the driver do the conversion, which seems to work fine.
But as much as I was prepared to hate this printer, this is a tremendous effort, and they got it mostly right the first time out. The software is quite good, the documentation is superb, and the printer (when set up correctly) produces some stunning prints.