Our long national nightmare is over: The ArduPilot Mega main board is back in stock. Sparkfun has 164 on hand, and more will be built as these go. The IMU shield is also in stock at the DIY Drones store, as are both the MediaTek and uBlox GPS modules. So basically everything you need is now available.
The code is in good shape in Alpha release (SVN only) and is being flown regularily. It will be released in public Beta (zip file) for less expert users by the end of Sept. The ArduCopter branch is also flying well, and should be ready for the commercial release of the full ArduCopter kit in about a month.