I'm a big fan of not making people register until they're already committed to your service. Maybe instead of asking users to "Sign Up" right away you can have them just "Try it out". Then once they've input some data if they want to save it they can create an account.
And since I didn't sign up for the service, how are you enabling users to share what they've created? This is key to building your user base.
Yes, I should work on that idea of letting the people try the app before singing up.
For sharing their map users have the option to embed it in their websites and blogs. There are two versions of the map: an interactive one (with Google Maps, which can be zoomed in) and a static image (which can be embed in places which doesn't support iframes, like Myspace or Flickr profile).
