You probably noticed, that Visual Studio creates new files in your solution folder whether you like it or not. One of those files is the Solution User Options file with the .suo extension, which contains settings specific to the given developer machine. You can delete it, but it will quickly grow back.
You have to be careful with these per-developer or per-machine setting files, especially because you should not add them to source control. Not a coincidence that *.suo is the first item in the .gitignore file recommended for Visual Studio projects.
Unfortunately .suo is not the only file like that, you can see many of these polluting your project root when you are using different project types. It would be much cleaner if all those files would live in a single folder!
Thankfully it is already solved in Visual Studio 2015, and the IDE puts them into a separate directory which is called .vs similarly to other development environments:
The .vs is a hidden folder so you have to enable the Show hidden files, folders, and drives option in Windows Explorer if you want to peek into it (but why would you?). Currently (Visual Studio 2015 CTP6) the .suo file and the Visual Basic/C# IntelliSense database files are living in this folder and its subfolders, but in the future releases more and more files will be moved here, and hopefully this practice will be followed by add-in developers as well. If you are upgrading an existing solution, the old files will not be deleted automatically, so your settings are not lost if you open the project later with an earlier version of Visual Studio.
The best thing in this feature is that this folder was not invented by the Visual Studio developer team. It is there because I asked for it. I and 2822 other Visual Studio users on the Visual Studio UserVoice page. The IDE team looked at it, thought it through, accepted it and implemented it.
It feels so good, when developers listen to the end-users.