We have a bunch of data on S3 (images) but just started reading about Mosso Files (rackspace). Sometime this month they are going to add CDN capabilities so any file you upload is part of the limelight CDN.
Anyone using this service, it's not as well documented or publicized at S3.
Yes, it's not well documented or publicized as S3. But dude it has CDN support which S3 is lack off (unless you willing to pay extra of course). Bad thing is you can't FTP into Mosso CloudFile, you will either have to upload it through web-based control panel or API. Yet, it's still cheap and worth especially with CDN.
I am using the service and it's pretty good and cost effective compare to S3.