The MightyOhm kit replaced a Velleman kit I had been using earlier. The Velleman kit was more expensive and of much poorer quality, not to mention, being a closed-source design and had a much smaller, less sensitive tube.
Here's a picture of the whole set-up, you can see the geiger counter at the right and the rest of the MCP at the back (click for full-size):
The MCP is based on an Arduino Mega, and incorporates ethernet, xbee, a couple LCD displays, and various remote sensors and controls. It still has lots of room for expansion, too! It is installed in a 'cubbyhole' in the upper part of my desk, directly over my computer monitor. The geiger counter is powered through the arduino, using the 3.3v line.
For this installation, I'm actually only reading the pulse output of the geiger counter, and doing the CPM calculations as part of the MCP's function. I'm using a fairly simple calculation method: it simply tracks the actual counts per minute for the past five minutes, and averages them every minute. So the CPM on the LCD updates once per minute and shows the average of the past 5 minutes. Not quite real-time but close enough.
And as of yesterday, it's now on Twitter. Radiation is tweeted hourly at the bottom of the hour.
The twitter feed is at http://twitter.com/M_C_P_
Cheers!