Cloud computing is one of the hyped up concepts of recent years which I'm really getting into, and even wasn't too much of a skeptic when it first emerged.
Why? Not sure... but does it matter? I only mention that because its my way of saying that I believe cloud computing to be quite a legitimate theory. I even find that cloud computing to have cultural significance!
Many companies have and are investing in "cloud infrastructure", including Amazon. They have many cloud computing products and services, and the primarily one I'm using these days is called Cloud Front. Its a content distribution network that uses Amazon's S3 service as the back-end.
I'm only using it minimally though - I have my own content distribution network which I prefer for most situation.