When an organization says they are "using the cloud", it can mean a
number of very different things. Using an IaaS service such as Amazon
EC2 or Terremark is different from using Google Apps for outsourced
email, which is different again from exposing an API into Facebook.
So here is a video of three Cloud Computing case studies from Vordel's customers. They cover one each of SaaS, IaaS, and PaaS. In first two examples, customers are connecting up to the Cloud; firstly to Google Apps (for single-sign-on to Google Apps email) and secondly to Terremark to manage virtual servers. In the third example, the connection is from the Cloud (a Facebook app) to a company's APIs. Here's the video, and see if you can spot the Animal House references :-)
I made the presentation using Prezi, so you can click through the presentation (minus the audio) up on Prezi.com.