I recently came across a Nikon NPC Proback II for a reasonable price. I wonder if someone could answer a couple of questions:
First of all, is instant film for it still available? If so, which ones?
Secondly, for anyone who's actually used an alternate Nikon back, just how much hassle is swapping them out? I wouldn't do it a lot, but it's something to think about.

In the case of the MF-12 Databack, I assume it prints the data on the emulsion side, similar to the option that most P&S's offer. (It would be great if it were on the back instead, but I don't see how they could pull that off.) Also, where on the image and what size is the imprint?