In the old days, when a new version of Visual Studio was released, many times, when opening an older project, it was converted to the new version and, from there, there was no going back. If you chose to make a backup during this process, you were ok.

What I found very nice was that, during the conversion process, the project was changed to the new 2012 version. However, it also retains the ability to be opened in VS.Net 2010.