This has always interested me. I need to do decently big storage for genomic data. It doesn't have to be fast, but it needs to be able to survive one data center blowing up. If I have 3 data centers, need to store 2-3 petabytes and need storage to survive in the case of a data center failure - the solutions really narrow down when you have to get under the $200/tb range.

Playing with Swift now - but it has really opened my eyes to how much more difficult 2-3 petabytes of storage is (disk failures, number of disks in your infrastructure, the time to redeploy a datacenter on a 1gpbs connection). All the little problems become much bigger!