FYI -

"A Fatal Flaw For Open Source"
(Dan Woods, 06.15.10, 06:00 AM EDT)

"Open source by and large was created for the single-tenant architecture. There are companies like Acquia that have created multi-tenant versions of Drupal for their commercial hosting service, but that was done by the founders of the project. I don't know if they have made the multi-tenant part of it open source. But it's a lot of work, it wouldn't surprise me if they kept it to themselves.

But the bulk of use of open source is not going to be easily converted to a multi-tenant form. So when you set out to create a Web app, which I argue is going to have to be multi-tenant to achieve scale, you are going to have to do a lot of heavy lifting."

Part 2 - where the quote is from:
http://www.forbes.com/2010/06/14/google-yahoo-software-technology-cio-ne...

Part 1:
http://www.forbes.com/2010/06/14/google-yahoo-software-technology-cio-ne...