While I waited for my ArduIMU and Mega, I broke out a 3 axis accelerometer and Arduino Pro I got from SparkFun some time ago. As an exercise in getting to know Ardiuno better I spliced together Kalman code from Jordi and accelerometer code from Ruben Laguna to make a simple tilt gyro, the video shows the results, accurate to +-45 degrees I think, not bad for a few hours work, can't say I understand the Kalman filter any better than I did 6 months ago :)..
I really like that the Mega has additional serial ports, this makes coding for the GPS or IMU, a bi-directional ground station, and other serial devices possible. I got my Mega and ArduIMU the other day and am looking forward to much fun. I wanted to try the 2.5 code with ArduIMU support but the code only includes uBlox parsing and I've got a EM-406 GPS. Anyone know where I can get a uBlox?