Sean Fujiwara recently posted a native extension for Adobe AIR at AIR 3 Native Extension Example – PenTablet.
This extension lets an AIR application get the pressure sensitivity data from a Wacom Intuos 4 pen tablet on Windows 7. It’s a good example of a Windows native extension that handles Windows messages and uses a native library — in this case, the pen tablet’s library.
Sean also provided another native extension for Windows that encodes a bitmap into BMP, JPEG, or PNG format using Microsoft .NET Framework 4. See AIR 3 Native Extension Example – ImageProcessor.
You can see more examples and tutorials of native extensions at the Adobe Developer Connection page http://www.adobe.com/devnet/air/native-extensions-for-air.html
Detailed documentation about creating extensions is at Developing native extensions for Adobe AIR.
To use a native extension in your AIR application, see Using native extensions in AIR applications.