I'm in the process of updating the landing page with more information on the way. Facebook is not mandatory for using the application - you can also signup using an email address. At the moment, this app is only for iOS.
To answer your questions:
* All data is stored in the cloud - i'm using Parse. Images are cached on the device once they are downloaded but data is always fetched from the cloud. This also means that you can get all your data if you delete the app and install it, or even if you switch to another iOS device. The UI provides an option to delete stories from cloud and you're in full control of your data.
* Right now, users can only share on Facebook. An update scheduled for this build will cover other platforms using Apple's Activity sheet.
* The screenshots on the iTunes store cover the steps that a user goes through to publish a story. With the next scheduled release, i'm also going to add a small video preview.
Thanks for your feedback. I appreciate the questions. :)