As part of the Decentralised Apps Hackathon and Unconference, I ported the noBackend Invoice-App example to SAFE today and published on the Alpha-11-Network:
Source Code on Github and Source Documentation right next to the App
In order to showcase the usage of it, they've implemented some examples - among them the invoice app, which uses a simplified interface that the specific "not-backend" then needs to implement for the App to work. Those actions are solely based on storing and retrieving content for a specific User. Clearly a prime use-case to do this with SAFE!!!
I am not sure if the Invoice App itself is really acceptable solution for people to use, but I inline-documented the code of the Storage-Engine to make it really clear and easy to follow how you could go about it.
I will also talk about this example at the upcoming Front-End Amsterdams Meetup.