Uh, no thanks. Would order--it's like buying a rental car. We all know how careful we are with rental cars.
I'd stay FAR away from this deal.
My .02.
It's always a tough consideration.
I've bought dealer demonstrators (cars the owners/employees have driven) all my life, only because the savings were tremendous (always much, much better than any discount -- even my GM employee discount!) and because the dealerships have historically taken care of them. My Suburban was purchased with 6,000 miles or so for about a 20% discount, for example.
I have also purchased former rental cars in the past when there was a good deal - my wife's car was a 2003 Chevrolet Impala. I negotiated a 25% discount from blue book value at about a year old (18k miles), and she drove that car for 6 years and put 120,000 miles on it. The only failure of that car was a BCM (body control module, computer that controlled interior stuff) that failed near the end of its life.
As for Tesla's pricing, though, I would not go for it -- it's not enough of a discount to me. It's not that I don't trust drivers of Model S (I think that Model S loaners are likely given far better care than your average rental car). If a loaner has 6,000 miles, a discount of 5% just isn't enough, IMO. Then again, Tesla doesn't seem to have problems with demand right now as long as they keep drawing new attention through things like the NHSTA results, etc. They'll likely have to change the pricing in the future, I believe.