Comment by VengefulCynic

I know way too many developers whose understanding of server infrastructure only extends as far as the API for S3. Marco's advice is dead-on: learn the nuts and bolts rather than becoming reliant on a leaky abstraction. You can always specialize to a specific cloud host after you understand the basics... much harder to go the other way if you've made your app reliant on Amazon or Rackspace-specific services.