I don't remember the discussion in USB Complete, but Jan also discusses it here:http://www.lvr.com/development_tools.htm
Basically, if you know that you're never going to release the device to the public, then you probably don't need to have a VID (Jan even allows researchers to use her VID in these cases, see the link above). Windows (and I'm assuming Windows only because you mention PnP), or any other OS for that matter, generally don't care which VID is used unless it happens to conflict with some other device on the system and as long as it can find the matching VID in the .inf file.
Also, some USB chip vendors allow use of their VID with assigned (by them) PIDs in certain cases on products using their chips. This is very manufacturer dependent and you'd have to check directly with them.
In a nutshell, if you plan to market this device, you really do need your own VID.http://www.usb.org/developers/vendor/