I don't use a lot of new consumer web apps for this reason (I did use Batch just to test, but didn't start using it heavily because I was afraid of something like this happening).

One way of reassuring me in using a product like this would be to have something in the app's settings menu that allows me to point to a different production server, and a commitment in the legal Terms of Service that in the event that the product is shut down, that the server-side code will be open-sourced.