In the wake of the Japanese nuclear disaster there has been a surge of interest in interfacing Geiger counters to home weather stations so that radiation levels could be monitored via APRS. When you think about it, it seems a very good idea. Even if the measurements were not of lab grade accuracy, they would be good enough to show what was going on. It could avoid unnecessary panic - and equally make it impossible for officials to hide the existence of a radiation leak - if data from a network of amateur radiation monitoring stations worldwide was publicly available. This could be a real application to make APRS relevant even to the general public.
A standard for representing radiation measurements in APRS weather packets is being worked out as I write. The question is how to interface a radiation monitor to an APRS system and what hardware is needed to measure the radiation? Unfortunately, if not surprisingly, the final bid price of dosimeters on eBay has gone through the roof in the last couple of days. But in any case they all seem to be standalone instruments with no computer interface. I don't know if a homebrew device would be possible, given that calibration would be needed, but if someone could develop one I think it would be a popular project.