Until Visual Studio 2012 Release Candidate, opening an existing project in a newer version of Visual Studio launched the Conversion Wizard. This forced an upgrade of the content (assets) of a project and solution to new formats that were not backward compatible. Therefore, after the conversion you could not open the project in the older version of Visual Studio.
Now with Visual Studio 2012, project sharing is possible between VS 2010 and VS 2012.
This means that if you open a 2010 project in Visual Studio 2012 , you will still be able to open the project in Visual Studio 2010 SP1.
Note: A few types of projects cannot be shared between Visual Studio 2010 SP1 and Visual Studio 2012 Release Candidate. These include some older projects (such as ASP.NET MVC 2 projects) or projects for special purposes (such as Setup projects).
When you open a Visual Studio 2010 SP1 Web project for the first time in Visual Studio 11 Beta, the following properties are added to the project file:
Hope you like this new features. Till the time enjoy the life and coding !!