I just saw on the Travel channel a new sport that has developed from technology called, "Geocaching." There is a N. CA based website that tells all about it and posts the details but the essence is this. It is a "hikers" scavenger hunt using GPS's. Some one hides a prize and clues, then gives out the coordinates to the first clue and the game is on.
So why not apply this to biking? A great deal of us have GPS's for our bikes, it seems like a logical leap.
Here are some of my thoughts. Some one either hides an item or supplies a prize of some sort (a restaurant - ie free lunch) at the end of the quest. Then either places clues along the way or uses landmarks as clues to the next area. After this, they post the prize and the coordinates to the first clue. Who ever gets to the restaurant first gets the prize or free lunch.
Seems like a great addition to riding. Maybe not a replacement to Poker runs, but certainly some thing else fun to take advantage of.