Other interesting Quadrocopter projects that use a Raspberry Pi:
A blog with many lessons learned on how to build different quadrocopters with a professional attitude and love for details. Much valuable background information is given! [german]
Good documentation on how to build and program a Quadrocopter, into the depth of PID controllers with Python.
This is really a very exciting Project because of the separation of concerns in different services, which can also be implemented in different languages (C or Python).
I would love to include some kind of SLAM technique with a Quadrocopter. LSD-SLAM seems very promising for this:
Because SLAM is really intensive in terms of computing power, it is not so easy to achieve on a Raspberry PI. Therefore streaming video to a groundstation laptop seems to be necessary. This also enables a cool live view for human beeings.