Blogs
Although software plus services is an emerging approach for delivering business solftware there are a number of Blogs that are focusing in the area. In fact in may be that as a new subject area it is blogs that provide the only decent source of information, but that will be for you to judge:
Links
Buying your Software as a Service? Make sure you ask the right questions (
Whitepaper)
Microsoft Partner White Paper (to
access this you will need a valid Partner ID)