Business logic in web-oriented application

Software Architecture Warehouse started as a web-based client-server application with major part implemented on the server-side. Ruby on Rails based back-end hosted persistence, business logic, and view generation. Client (web-browser) was merely responsible for rendering server-side generated views. Over time it became clear that this set-up is not capable of fulfilling requirements of highly-interactive collaborative usage.
Today, weight of SAW shifted dramatically towards the client-side. Thanks to application of frameworks such as Backbone or Marionette, user interface rendering moved completely to the client-side. One of the hesitations that I had recently was where to position application business logic.
In fact I find it useful to speak of two kinds of business logic:

• presentation/view oriented logic - can and should be implemented on the client-side, because this way it offers very good responsiveness (low latency) and thus good user-experience
• data/process oriented logic - can remain on the server side, because of the data access security and consistency concerns.