Well my two cents are that you do not ever have to buy the pass.
The adventure pass falls under a demostration program called the Fee Demostration Program. Since it is a demo, there is no legal right to force you to pay the fee, there is nomlaw to enforce it with. If you do not have a pass, you may recieve a notice of noncompliance, this is not a ticket and carries no penalty. The forest service, blm are trying to intimidate the public into buying the program.
A little current info: Bush in his latest bugjet proposal wants to make fee demo perminant and at the same time he is cutting the forest service bugjet by $75 million. Over the year 2000 the forest service claims to have made $25 million from the fee demo program, now any math wiz can see that they are not making enough
money from the program. So why the bugjet cuts? The end result will be the privitization of OUR public lands due to lack of proper funding. Get ready to have thousands of Mike Castro types controlling and charging us to access public land.

check www.freeourforests.org listed as a link on this site