Today on my way home I read an article from The Architecture Journal devoted Service Delivery Platform. This is the same as SaaS but from a little different point of view.
Efficient Software Delivery Through Service-Delivery Platforms by Gianpaolo Carraro, Fred Chong, and Eugenio Pace
Summary: Delivering software as a service (SaaS) has gained a lot of momentum. One reason this one-to-many delivery model is attractive is that it enables new economies of scale. Yet economy of scale does not come automatically; it has to be explicitly architected into the solution. A typical architectural pattern allowing economy of scale is "single instance multi-tenancy," and many Independent Software Vendors (ISVs) offering SaaS have moved to this architecture, with various levels of success.
There is, however, another means of improving efficiency which ISVs have not adopted with the same enthusiasm: the use of an underlying Service-Delivery Platform (SDP). Adoption has been slow, mainly because service-delivery platforms optimized for line-of-business applications delivery are still in their infancy. But both existing and new actors in the hosting space are quickly building compelling capabilities. This paper explores the goals, capabilities, and motivations for adoption of SDP, and describes the technology and processes related to efficient software delivery through SDP.
In addition I have to make a note that the article is quite intelligible and makes many things related to SaaS clear. My verdict - RECOMMENDED