I am big on developer productivity and features that save me time from managing the development environment allowing me to focus on the task at hand like reviewing code are excellent examples great developer productivity.
I am currently reviewing a demo for Single Page Applications (SPA) using Web API 2 and Angular.js from github (https://github.com/MarlabsInc/webapi-angularjs-spa) where I am exploring the project and realized this feature that I never really paid any attention too.
The ability to preview files in Visual Studio 2013 is great when browsing threw source code. In older versions of Visual Studio I would have to double click open the file and then close it again.
Today I just click the file browse and move to the next one without having to explicitly open it.