It is called "Architecture Strategies for Catching the Long Tail" and for me it is the best paper about this topic so far - and I like the the way Frederick Chong and Gianpaolo Carraro view the SaaS world with a mixture of de-mystification and what the opportunity could be. I very much like the architecture maturity model.

Last week I gave a presentation on it at a hoster seminar in Stockholm.

The paper can be found here