Ever since the Sea Otter Classic I've been donating my mileage through a cool site called Plus 3 Network. You select a charity to donate to, I'm donating to the IMBA (International Mountain Bicycling Association) and, because I don't have a swank GPS unit to do it for me, I enter my rides in by hand.
But if you've got a supported Garmin GPS unit, the system does it all for you AND donates triple the amount of a hand entered ride.
It isn't hard to do either way though and it makes the rides that much more worthwhile.
I am Erik Orgell on the site, join up and we can become pals. Or just join up and put your mileage to better use. And, oh yeah, free to join, free to be a member of and free to donate, as in someone else makes the donation based on the number of miles that you ride, run, swim or walk.
Get to it!