The sweet spot so far looks to be 25. The really fascinating data is slicing it up based on type of user, where they were referred from (Daring Fireball users will pay more than TechCrunch), what price they were shown versus what they want to pay, and of course how many blogs they have. There's also the clever guy from YC who put in -$500. :)
There are available alternatives and I wouldn't think backups provide any social status, so I don't think higher prices would mean higher demand.
But maybe... that's why I'd love to see the results (even just as an anonymised chart of price/demand).
The relationship between the "planning to charge" price shown and the price someone volunteers to pay in the "perfect world" would also be interesting.