I bought few of these about a month back. They are much lighter than the normal Arduino board due to the use of the small USB 2.0 header and surface mount chips. I'll weight both and post, but if you are looking to build a mikroquad, or anything where weight is an issue and you don't happen to be using the ArduPilot (which is already really optimized for size!) this is a good alternative. Oh, did I mention it adds two ADC pins to the normal arduino configuration? Really nice if you want to add… Continue

Wow, I can't believe I missed this one. Someone has been working (HARD) on an Arduino based quad.

http://mikroquad.com/bin/view/Main/WebHome

Their source was put up on the 21st of December

http://code.google.com/p/mikroquad/

Looks like a great start. I need to get my planes finished so that I can build one of these too!

With some simple sensors we could detect the pitch and altitude to make better decisions about altitude changes and what to do with them. I'm thinking 2 sensors from sparkfun would do the trick.