http://www.educause.edu/EDUCAUSE+Quarterly/EDUCAUSEQuarterlyMagazineVolum/CloudComputingExplained/206526
We have all been beseiged with information on cloud computing; SaaS, Iaas, Paas and other acronyms. Educause has pulled this all together using the official National Institutes of Standards and Technology (NIST) definition, in a really understandable document.