One of the new features in VS2012 is the ability to 'preview' a file instead of opening it fully which will open it in the 'preview' pane (docked to the right). To do this Left click on the file in the solution explorer. The great thing about it is that you can only have one preview open at a time. So when you're searching for something looking through several files in the process, the ones that aren't needed will close themselves.
As cool as it is, it started to annoy me after a while as I click in the solution explorer to enable scrolling if I'm out of Visual Studio. If it happens to be a large file it can take a second or two to load. So I went looking for a solution and it didn't take long to find one. Alt + Left click in the solution explorer will not show a preview of the file.