As the title suggests, I'm wondering if debian (or any linux) can be configured so that the USB ports (or just 1 port) of a debian host can present itself to another host (windows? mac? hardware appliance) as strictly a mass storage device? The idea is to be able to plug USB on debian to the USB on another host and have the other host detect it the same as if you plugged in an external USB drive.

You can not directly connect a USB cable between two PCs. There are special USB cables that are called host to host or bridge cables. It would be similar to connecting two PCs via an ethernet crossover cable. In theory it should be possible to build a cable device like the host to host cable that would simulate a storage device but I have not seen one.

Not quite what you asked for but I think this will work, no idea how to do it though,

make a folder, lets say /share

now share it over the lan as a NFS or Samba share, if you want add a username and password and limit it to one IP address.

now all you have to do is configure the automounter so that a symlink is created inside /share pointing to any usb in the right socket.

then just access it in my network places (or entire network) from windows.

Tortanick, the device I want to attach via USB only recognizes mass storage so using nfs or samba will only work if Linux can somehow present what you describe as mass storage.

michaelk, are you saying a cable configuration can permit a host OS seeing "mass storage"? I mean, I understand that I have to do some USB to USB adapting so the data can flow from host2 to host1, but what I can't find is how to make their communication be host1 <-- mass storage[host2].

The only lowbuck NAS I've seen in the market place are ethernet based OR usb based. But never both.

Not impossible but a special cable would be required for a PC to be recognized as a mass storage device. I am not aware of something like this that one can purchase. I was suggesting networking two PCs together via a special USB cable.