What are the best practices in building applications that support multiple tenants such as Software as a Service?
Links to white papers that expand on this topic are greatly appreciated.
You might find some valuable advise in a series of blog posts by Oren Eini.
This is one of the last posts in the series, with links to previous posts: http://ayende.com/Blog/archive/2008/08/16/Multi-Tenancy--Approaches-and-Applicability.aspx