Just because client-side rendering did not work well for Twitter for a variety of reasons, does not mean it is subpar to server-side rendering in all cases. Performance-wise, if server_json_generate + json_download + client_render_json_to_html < server_html_generate + html_download + client_render_html, you can certainly go with client-side rendering.

In Twitter's case, client-side rendering was slow while server-side wasn't. In LinkedIn's case, html_download was slow while client_render_json_to_html wasn't. Performance aside, there are numerable reasons to go either away, all of which vary from project to project.

Having Worked with CoffeeScript + Twitter Bootstrap + BackboneJS/Underscore + LessCSS for some time now, I know I will not willingly go back to the old server-side ways unless there is a major reason to. Working fully client-side to make UI and relying on REST API / JSON is wonderful experience, especially when the app feels so responsive.