Here’s some amazing videos of research quadrotors.
http://www.youtube.com/watch?v=UQzuL60V9ng
http://www.youtube.com/watch?v=S-dkonAXOlQ
See video in post 21. You might really enjoy it.
I am thinking of building a KK2 based quad. Every couple of months brings more capabilities in new releases of the firmware. GPS function is a little immature at this point, however.