I wonder if Bill will collect green stamps. I wonder if the "credits" homepage links to an optional interactive page, where you can open and page through a "virtual stamp book," and paste your credits into it, as "green stamps."
On how you exchange your "credits" for something you'd possibly want, explore the entire Bing Rewards page and its links; but I'd guess you could save all your credits for Christmas and buy yourself socks and underwear. For online delivery - virtual goods? I think that's where the tangible might intervene. Does Amazon.com sell and ship socks and underwear, or do you need to go to Walmart online, or Target online?
_____________UPDATE___________
For those too young to remember green stamps, think, frequent flyer miles.