An USB stick, if formatted as USB ZIP disk, will make possible on some motherboards to boot from it, let's call it "rudimental low-level" emulation.
Well, agreed.
If you want an USB stick, formatted as USB ZIP disk, to look like a USB ZIP DISK in windows there are "cosmetic" changes you can make:
http://www.virtualpl...ml/icn_drv.html
let's call this "rudimental high-level" emulation
Agreed.
Of course the Vid & Pid of the Device will remain the ones "carved in stone" in the USB stick hardware.
Yes.
If you want a "more accurate" emulation of a ZIP disk, you can write your own Filter Driver or directly a "USB-stick-driver-that-behaves-like-a-ZIP-disk", this would be "complete high-level" emulation.
Rather "pretty high-level software emulation", works only in Windows.
In other words, a real mode OS like DOS will treat a USB stick just like the USB ZIP disk, as it has no means to "tell the difference", i.e. like a normal volume, a "protected mode" OS, like Win9x/Me can use a device driver (in this case written "ad hoc") to access the device, on NT based systems, thanks to the HAL, EVERYTHING is "virtual", so you can use a Filter Driver or a Kernel Driver to make the OS think the USB stick is a ZIP disk.
Yes, a filter driver is possible but needs very much work, to much for me.
So, I do get your point, but I am still wondering what would be the practical consequences of wasting a few weeks work to build a such a Filter or Kernel driver? 
Not talking about such a driver but the point of these features in general. You asked me before, now I have more time and just for your curiosity and interest I am glad to tell you about it.
I hope I remember the most important points I thought about.
USB-pendrive or 2.5" USB-HDD in general:
No external power needed, very small, handy, stable, fast and powerful even in pocket.
USB-HDD booting:
This is a bit messed up for DOS or NT booting. The booted device becomes the grub device hd0,0 and device letter C, while the internal IDE/SATA 0,0 and such devices will be a bit messed up with numbers and letters. In DOS it's a bad idea to load further USB drivers after booting from USB-HDD. On NT like operating systems some applications (harddisk undelete and check) get confused (ok, I doubt it will be different in USB-ZIP mode but unsure).
USB-FDD emulation:
This is best if you have legacy software which wants a floppy drive A:, it's fully bootable (if USB-FDD boot supported) and a 90 % floppy replacement (not just workarround). I like more mature replacement solutions rather then fiddling. Also great for creating bootable disk (dos, backup, virusscan, special purpose, server, recovery...). Very good compatibility.
USB-ZIP emulation:
Also good compatibility and good for a full collection of tools for recovery, special purpose and such. Gives you drive letter A:, therefore no mess with displaced drive letters. With USB-FDD and USB-ZIP you can also load USB drivers in DOS without creating a disaster after booting already from USB because these devices are ignored by the drivers. This seams to be also the best place for a (emergency) bootmanager for multibooting.
USB-CDROM emulation:
Great for 'netbooks' (very small and limited notebooks) without real CD-ROM, you can use it to install operating systems without CD and without CD-ROM in a very easy way. Also nice for portable use (CD autostart is working and readonly). Any special CD's can be also 'burned' onto such a device, also protected mode stuff possible.
The spreading of this features is not very widespread. Very little USB-pendrives support it and currently no known USB-HDD enclosure. Therefore I think I need to live with the known workarrounds, it was worth to ask in the forums for knowledge anyway.
(any device, such as this USB-pendrive) claims to be 
(real USB-ZIP).
(real USB-FDD).
.
