Check out this video from the Salesforce "Future of Software" event in London on the 13th September. (There could be a need for a leaving contact information to see it.)
The event is two hours, but you're able to jump between the different parts.
Marc on the SaaS model: fast forward to 64 minutes in to the presentation
Click on the Carbon Trust in the menu and wait to Marc is back. It's also possible to click in the timeline box to jump in the presentation.
A business case: take a look at the Total Jobs presentation (by the way, this guy has brilliant presentation skills!)
Source: found the video at the "Where is the upside?" blog