At the moment, Ractive doesn't really have an opinion on the subject - it was initially developed with news interactives in mind, where very often there isn't a need to communicate to a backend.

Backbone et al are better at handling that side of things. The Ractive approach is to use an 'adaptor' - so you could create a Backbone Model or Backbone Collection adaptor that maps to a particular 'keypath' (such as 'user' or 'items'), and whenever the model changes, Ractive updates. With two-way binding, user interactions can also change the model.

This part of the library is underdeveloped and experimental at the moment, but that's the approach we'll most likely be taking.

You can use Ractive on the server however - you can use the same data on the server as on the client and call ractive.renderHTML(), which is useful for progressive enhancement.