I don't know a whole lot about the backs because most of what I know is from personal experience, and since I haven't had the chance to mess around with much more than 35mm (other than with toy cameras or my TLR), I haven't yet had the chance to use a Polaroid back either. The only thing I've heard is that most of the MF SLR cameras take the backs that support Fuji's 100 series film like you said. If I hear more, I'll let you know, but for now, I'm trying to get all the personal experience I can through handling the hardware myself. I have the opportunity to borrow a Mamiya M645, but I hate borrowing equipment. I always feel like I'll have an unlucky experience with it and have to give it back with something wrong with it. Maybe someone would be willing to trade one of their SLRs for some of my stuff.