For those new to the concept of cloud computing, it is similar to the concept of leveraging disparate functionality in a SOA environment. However, in this case the Oracle Database and Middleware products are hosted by Amazon, and the database and middleware functionality can be leveraged as a service. (A picture would explain this better... future post). Lookup EC2 (Elastic Compute Cloud) and AMI (Amazon Machine Images) for more information.
These are powerful new development in this uber-geek domain. What it does mean is that databases are being commoditized and you could essentially use a database in the same way as you use a telephone. Sounds surreal... so did SOA 4 years ago.
Footnote: Don't imagine these clouds to be white and fluffy... darkish grey and Amazon-shaped would be more appropriate.