Wow, this is really impressive! A whole year without any new storage for such a large enterprise is downright miraculous.
I suspect that Flickr's past the explosive growth stage so an optimization like this is timely.
When you have a database which keeps redundant master slave replicas and mutation logs, a backup system which keeps many previous backups on-site and offshore on tapes, a storage system that has many RAID mirrors per host, a distributed filesystem which stores replicated chunks of data across an entire datacenter to handle host failure, and you keep copies of the entire lot in multiple datacenters for accessibility during planned downtime and natural disasters.