The main pro for storing data in the cloud. Let's say on Amazon S3 is that you also get a web server that is able to serve those same files (public or secure).

The main pro for storing data in the cloud. Let's say on Amazon S3 is that you also get a web server that is able to serve those same files (public or secure). Even if you need them served to millions of users. You don't have to care about scaling this thing. Good luck doing this with a NAS.