There are no known "screw up a working back" issues linked to the latest firmware upgrade that I've heard of. I've upgraded all three of my Hasselblad backs to good effect.
Linking Jurgen's issue to the firmware is jumping to conclusions not supported by information, by Hasselblad tech, nor other people's first hand experiences.
What I would caution is following Jurgen's order of loading the firmware.
For now, I would avoid hooking up the back via firewire and then powering up your PC. I was shown how to do this and it wan't in that order. I was told to start the computer, connect the camera with the firewire, then start Flexcolor... at which time Flexcolor should recognize the back, beep with audio confirmation, and then prompt installion of the new firmware with each step clearly communicated. Miss a step and you are in for trouble. (BTW, copy the old Flexcolor on a separate HD, in case you want to return to it for some reason).
I have a call into my dealer/tech to check this, and will report back when I get an answer. It may be nothing, but I've found that you have to do things the way they say to do them.