I'd add a "how we make money" explanation somewhere. I'd imagine most people that'd be interested in this would be wary of "free" (i.e. whats the catch).
But I understand some people are wary of "free". I would be too. I'll do a writeup about this topic and make it available from the homepage. Hopefully this will convince people that there is no hidden cost or catch to using Scribbble.
If you created this service on a whim, what’s to stop you from taking it down on a whim as well? Accepting payment also serves as an establishment of trust in this regard, I wouldn’t just simplify it to “accepting money is bad”
I don’t mean to negatively criticize your service, I think it’s neat! You just might need to ask yourself some more questions like this to justify hosting people’s data