I am currently in the process of documenting the Programmer's Guide and the UX Guide, and admittedly there are some items that are out of date. The API documentation included with the SDK and available at http://developer.garmin.com/connect-iq/api-docs/ should be fairly up to date, though perhaps not as complete as some would like. :)
Is there a particular feature you are having difficulty understanding because of poor or outdated documentation?