The unit uses an Extended Kalman Filter for yaw, pitch, and roll estimation. It doesn't do centripetal compensation, but I routed out an extra UART and an SPI bus for anyone who wants to add extra sensors. I was thinking specifically about GPS when I selected the on-board regulator - it can supply up to 400 mA of current, which should be enough to power whatever GPS unit you wanted to throw at it. The firmware is open-source.
I'll be selling them from my website by the end of the month: http://www.chrobotics.com. If you want one, contact me directly and mention that you are a member of DIY Drones - I'll drop the price for you. :-)