Think of the change we had when web technologies able to migrate from static to dynamic contents, i can compare this to such a revolution where as cloud computing provides ability to consume resources dynamically.
No wonder Gartner has predicted 'Cloud Computing' as top strategic technology that most organizations will drive for during the year 2010 http://www.gartner.com/it/page.jsp?id=1210613
Few factors that drive cloud computing
1. Effective utilization of resources
2. Capacity on demand
3. Pay as you use model
4. Green IT
5. Reduce expense on hardware