Well, just a few days after i updated my images site, Amazon post a tutorial showing you how to do it! Pretty cool, and fairly close to what i have done with mine. A few differences:
1: the Amazon demo uses the S3 URLs in their pages, mine has a redirect in the ASHX file.
2: They generate Thumbnails for the images, which is a nice touch, but most of the time is not required for the images I upload, so i probably wont implement that anytime soon.
3: they are using an Access DB for storage, i have a full SQL box.
4: their code is available now! eventually mine will be, but that might take a while…