that's the most realistic post of them all. And basically what he says here, is what everyone should be doing. Design for your objective, your message, not for a trend. Use flat elements if they are an advantage to your project, use realism if it benefits your message. Basically, use whatever you want that may help you accomplish your objective.
http://www.matthewmooredesign.com/almost-flat-design/
This points out how important and useful the subtle and tasteful use of gradients and shadows can be within flat designs.