I thought I'd give some useful information about the docs we released for PDC.
Keep in mind that these are very early docs. The docs for the Sensor API, Location API, and Sensor WDK provide some pretty good and mostly up-to-date reference materials, but the overviews are very sparse and programming guide material is non-existant. The WDK docs tend to be more complete than the API docs. We focused there because the API is certainly more useful when hardware drivers exist for sensors that you can actually use.
If you want to understand the platform-defined sensor categories, types, data fields, etc., you have two options: look at Sensors.h or refer to the WDK documentation. The WDK docs contain a whole reference section on constants, complete with descriptions and even some recommendations. This information is not present in the API docs, yet.
The WDK has some example code in the reference topics. The Location API also has some examples in the scripting reference topics, particularly showing how to instantiate the objects.
If you were lucky enough to get a Windows 7 Sensor Development Kit at PDC, then the sample code we provided there should be a goldmine of information for you about how to use the driver and client interfaces.
Keep checking back here as I post more information about how the platform works. I plan to post plenty of code, too. And we'll have more official documentation at beta and beyond.