I recently purchased the HP8600 from Costco (thankfully), and have been working on getting it set up with all of our electronics in our house. (i.e. connected to my wireless network, and all of our related computers). I bought this device primarily to consolidate a canon printer and a xerox multipage scanner.
I currently run a Macbook Air using both Mac OS and a Windows 7 Virtual Machine using VM Ware's Fusion product; and my wife runs a Macbook Air using Mac OS. Printing has worked great. Scanning has not worked that well.
I have found that the scanning functionality of the HP8600 freezes regardless of whether I am using Mac or Windows. I would actually diagnose this as a firmware/hardware issue. When using the document feeder, the scanner freezes in the middle of a document set. The device stops scanning, the screen on the devices continues to show "Now scanning..." and the computer eventually states the the scan is complete.
Using Windows 7:
This happens with the HP Scan application or with another application I use called PaperPort 14.
This happens with 3 documents or 10 documents (i.e. is # of documents isn't a cause)
This happens with the HP Scan application.
The only way I have found to successully resolve the issue when it happens is to pull a half scanned document out of the device manually, and then power the device on and off.
If anyone else has had this experience and been successful with other resolutions, I would like to hear about them. If I can't resolve this in a week or so, I plan on returning the device and purchasing a different brand.
Try using the Image Capture program on the Mac. If that works and you still want to use the HP software, make sure you get the updated HP Scan 3 program on the Mac. I'm using Version 3.7.9 successfully. If using Image Capture doesn't work any better, it may be as you suspect, a problem with your particular printer.