Good news: APM 2 preorders have reopened. You can now choose it with the onboard GPS or without, so can use an external GPS or any other supported GPS module (the Ublox GS406/407 can be used with this adapter, and other modules can be used in NMEA mode).
All the necessary components for this batch of APM 2s will be coming in by the end of March, so pre-orders placed to today will be shipping in 4-6 weeks. After this pre-order period we will be in full APM 2 production, so the product should be constantly in stock by the middle of April. At that point, we'll probably also offer versions with external magnetometers, and with an option for different connector pins, including right-angle pins.
We also now offer a version with no pins pre-soldered at all, for those who want to configure it to taste themselves.
You can always follow the 3D Robotics Twitter feed for more regular updates.
On the code front, the current ArduCopter and ArduPlane supports APM 2, but has not yet been optimized for its sensors. Optimized code will be out in the next couple weeks, and further enhancements will be coming in the months to come. There's a lot of power in APM 2's MPU-6000 sensors, and you'll find that each software update taps it more.
The first code enhancement, coming in the next week or two, will address the "lean" issue that some people are experiencing on multicopters. This is due to vibration. With the current code, the APM 2 board is more susceptible to this for two reasons: first, because it's a lighter board than APM 1 and as a result has less mechanical damping even when mounted on vibration-insulation, and second because we have not yet implemented software filtering of accelerometer noise.
The reason for that second issue is that in the current code, most software filtering is done in the ADC library. But because APM 2 uses digital sensors, unlike the analog ones on APM 1 (which go through an ADC), it doesn't use the ADC library. This week we're going to move the filtering to the main ArduCopter code, which is shared by both APM 1 and APM 2, and we'll be able to optimize the settings for APM 2. This should resolve most of the "leaning" issues with a simple software update, which should be out by mid-March.
There are a bunch of other improvements we're doing to improve filtering, including new test processes and easier ways to adjust the filters, both for the dev team and end-users. We're also preparing to use the MPU-6000's internal DMP processor, as an option to replace the software DCM sensor fusion algorithm we now use, but are still working with Invensense on a legal path to distribute the source code, in keeping with our commitment to open source. Look for that update to be out in a few months.