I can offer no suggestion as to how exactly Maemo Mapper could have caused this.

Maemo Mapper runs in the (protected) user account (as opposed to the privileged administrator account), just like any other program, so theoretically it is impossible for it (or other normal, non-OS programs) to destroy the rest of the operating system. At worst, programs can corrupt user data (i.e. in "Documents", "Videos", etc.), but application code (including the OS itself) should be protected from corruption by a rogue application. That is the Unix way, and it's why Windows has recently tried to follow suit with the introduction of Vista's security features.

So, either Maemo screwed up and allowed Maemo Mapper to do something it shouldn't have been able to do (and I'm not sure what that would be, unless you manually invoked the "Reset Bluetooth" feature), or Maemo screwed up and took Maemo Mapper down with it as collateral damage. The latter, more systemic option would also explain why none of your other applications work, including the OS programs like the Application Manager.

Unfortunately, neither of those explanations provides for a solution. The first thing I would try is properly switching off your device. It sounds like you haven't been able to do that (because "the hard button won't cause it to shut down"), so try either letting the battery run out or removing the battery entirely.

If you still have problems, I can think of no other solution for you than, as you suggested, re-flashing your device. If you continue to have problems after you re-flash, then it is a hardware problem for which (unfortunately) you must send the device to Nokia for repair.