Amazon, as you might know, has EC2 for on-demand computing and S3 for on-demand storage.   A huge problem was that EC2 storage was non-persistent, forcing you to use S3 for storage.  There were workarounds such as RightScale and PersistentFS.    That has changed with Amazon's introduction of EBS (Elastic Block Store).  Volumes from 1 GB to 1 TB can be mounted -- read this post on GeekZone for more details.