Thanks for the responses, yes even thanks to you, Illuminatus, because yours made me laugh.
JHL, I have seen such rewards type programs, but the ones I have seen are not that engaging in and of themselves. With this idea, the quality of the game becomes key to its success. Imagine Farmville, which has over 60 million users, but with a nobler purpose.
To Hemlock, I like your scavenger hunt analogy, and I think you highlight one my main points, people like communities, they like doing things with others, and going on a cool adventure with others would be fun.
And finally to Illuminatus, I do realize that there are some people who have been enlighted (or illuminated) to the degree where they get such inspiration from life, but I think the world could use a few more such folks.