We have done a fait bit of work on the SaaS multi-tenancy problem in my team - Gianpaolo and Fred have spent more time thinking about this problem than almost anyone else that I know - we have published more architectural guidance than anyone else in the industry and just recently shipped the Litware HR SaaS reference application that illustrates the best practices for this problem space.

But, every once in a while I ask myself - whither multi-tenancy?

Will platforms provide native support for multi-tenancy? will virtualization be the means to achieving multi-tenancy in the near-term future?

Personally, I am more interested in the latter option - the challenge is managing the virtual environment(s) of course.