Interesting approach. Could you clarify a few things?
When you lease it out, what parts of the site do you modify for your customers, and what do you place off limits to them? I'm thinking you most likely don't allow them to modify the pages you've built up great SE results for and incoming links to, right? What would be the customers content/branding/advertising .vs your stuff; i.e. what about the site would change if you switched customers?
How do you price the offering?
Any tips on what to look out for when dealing with people with such an arrangement? How do you keep on top of things with them?