A few weeks ago, John deVadoss (my manager) and I recorded a short podcast introducing the key aspects of SaaS architecture. In this 11min. discussion, we briefly touch upon the ISV perspective, the Enterprise perspective and Hoster perspective.

A slide deck that somewhat illustrate this discussion can be found here. Whitepapers on this topic are available at http://msdn.microsoft.com/architecture/saas

Enjoy!