[ugh]

Show me what I can do right at the start. I know it's hard with this specific type of service, but some kind of screenshot or visualisation of the what you can do would be helpful. I don't know if it would work, but one idea I find quite intriguing would be some sort of reduced live demo right at the start page. I honestly didn't really understand what you were offering until I tried it out, so this seems to be the easiest way to show what you can do.

And what does registring get me? If nothing, then don't even allow it, if something, then show me what.

By the way, I really love that you fill the generate form with sane defaults. You don't even have to think about filling anything in and can just start to see what it's all about. Lesser sites would annoy you with stupid "Required field" warnings.