Japan’s difficoult moment has challenged many Arduino users (I can count at least three different threads on the forum about geiger tube & sensors lately  1, 2, 3). As David posted some time ago, the need of an open, net-spreaded visualization of the real level of radioactivity was heavily felt by the community, also for  trasparency reasons.  This is when the Geiger shield comes in:

This is an Arduino-based geiger counter shield that makes it easy to upload data to the internet and also interchange tubes. Since it’s open source and Arduino-based, its also easy to hack this to other interesting applications.

you can follow on  [TokyoHackerspace] the all process of prototyping.