In our office, we have an HP OfficeJet Pro L7780. This is functionally very similar to the 8500 model (although it has the optional hi-capacity extra tray too). I liked it so much I got a L7680 for home, too.

To answer the comments about Linux: HP may not provide Linux drivers, but Linux provides OfficeJet drivers. The OfficeJet Pro L7780 and L7680 work very well indeed under Ubuntu. In fact, the latest Ubuntu (9.04) automatically detects the printer, works out how to connect to it and installs the necessary drivers using UK defaults (for us in the UK, anyway). I imagine that the experience for the 8500 will be similar, although you might need to persuade it the printer's an L7680 if it hasn't heard of the 8500 yet. Doubtless the proper printer description files will be along very shortly if that's the case.

I agree about the duplexer. It does look an afterthought, yet the duplexer unit has been a standard fit on most OJPro printers since forever. However, the simple removal (press in a button at either side) makes for a very easy fix on the rare occasions the duplexer gets a paper jam. It does increase the printer's footprint, though, adding 6cm to the depth at minimum, or 14cm if you want to open the back flap for maintenance. These aren't printers you can put on a shallow printer trolley!

It sounds overall like the 8500 is a small step-change onwards from the excellent L7680/L7780 units. If that's so, I can heartily recommend them. Do keep a spare set of ink tanks somewhere. You have to change them so rarely that it's easy to forget to keep stock!

(Declaration of interests: none, just a very happy customer.)