Cloud computing provides service abstraction at different levels. You don't need to think about servers at SaaS (Software as a Service. e.g, Google Docs/Apps)

Cloud computing provides service abstraction at different levels. You don't need to think about servers at SaaS (Software as a Service. e.g, Google Docs/Apps) and PaaS (Platform as a Service. e.g. Google Apple Engine, Windows Azure; Amazon S3, Elastic MapReduce etc.) level, but you do have (virtualized) servers when you need IaaS (Infrastructure as a Service. e.g. Amazon EC2, VMware infrastructure) where you need to put existing/legacy applications that have clear dependencies on explicit servers in the cloud.