@overlander: Do you have any insight to these questions?
If the ratings aren't maintained by an official authority what about the trails themselves? Is it all done via by volunteers? I'm trying to understand how much trust I can put into the condition and safety of these trails.
How do I know what PSI to air-down to when out on the trail? Is there a standard set-it-and-forget-it PSI that is suitable for most green and blue trails?