AIR 1.5.1 was released on 2/24/09. Although it was a minor release, there were a few enhancements that you should be aware of.
New event that indicates if the application was launched manually by the user or automatically at login
The InvokeEventReason class (in the flash.desktop package) defines the two possible string values for the InvokeEvent.reason property. InvokeEventReason.LOGIN defines the login case; InvokeEventReason.STANDARD defines the standard case.
Jeff Swartz wrote a new quick start to explain how to use this new functionality.
- For Flex developers: AIR application start-up options
- For Ajax developers: AIR application start-up options
New property to return processor architecture
This new property (Capabilities.cpuArchitecture in flash.system) returns the processor architecture of the machine, as a string (such as “PowerPC” or “x86″).
Using these new APIs
If you want to take advantage of these new AIR 1.5.1 APIs, update your application descriptor to use the 1.5.1 namespace:
xmlns="http://ns.adobe.com/air/application/1.5.1"
If you do not need to use these new APIs, you do not need to update your application descriptor. Your application will be able to run with AIR 1.5.1 when the user updates the version of the runtime installed on their system.
You can find all the current AIR docs here: Adobe AIR resources

Where’s the schema forhttp://ns.adobe.com/air/application/1.5?
You can find that in the Flex or AIR SDK. The Flex SDK (which includes the AIR SDK) is installed with Flex Builder of course and you can find the schema in the \templates\air folder. If you don’t currently have a version of the AIR SDK, download it here: http://www.adobe.com/products/air/tools/sdk/.