I flew my ArduPilot V1 in a 33inch wingspan redi-board foam plane on numerous occasions with great success early last year. RTL and way point mode worked great after lowering the gains for the small light craft. Of course it only flies well on calm days since it had no stabilization. I retired it a few months ago and am building a pusher this time, 50-60 inch KFM3 wing, the fuse and tail modeled after the Raven UAV. If it flies I'll post picks :), the wing is built, and the fuse will be ready by tomorrow for some manual flight tests. I've had my ArduPilot V2 sitting on my workbench for far too long, I fly near some hills and frequently in a canyon and wanted to wait for an IMU version.
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?