Quick Answer: It has a hidden file attribute applied. Changing the folder options to ‘Show Hidden Files and Folder’ revealed the SUO file adjacent to the solution file .
When you open a Visual Studio Solution file, i.e. MySolution.sln, a corresponding MySolution.suo file is generated. This file is constantly updated with the current state of Visual Studio (i.e. which windows you have open). When you close and reopen Visual Studio, the previous state is reloaded from this file.
Unfortunately from time to time this can lead to problems. For example, It is common for Visual Studio to crash when too many designer files are opened simultaneously. Because the state is remembered in the SUO file ; it can then become impossible to re-open the Visual Studio solution because it will result in a re-occurring crash. When this occurs I usually just delete the SUO file; and Visual Studio will re-open a solution afresh; without any retained state.
However in Visual Studio 11 Beta I could not find the SUO file? Its normally would be found in the directory adjacent the solution file; yet I could not see it. I ran a search for SUO files on my C: drive and found none.
Thoroughly confused I opened ProcMon.exe and watched what files Visual Studio was loading as I opened my solution. A quick search found the suo file where I had expected it; adjacent to the solution. However the file had a hidden attribute applied to it so I couldn’t see it with the default folder options in Windows 8.
Changing the folder options to ‘Show Hidden Files and Folder’ revealed the SUO file.