Building Windows Phone 7 projects. Don't go to Visual Studio 2012
With availability of Visual Studio 2012 (VS12) RTM via MSDN Subscriber downloads, I decided to upgrade to it and to keep my machine clean, remove Visual Studio 2010 SP1. A mistake that I will now need to fix. You cannot open, edit, build and test Windows Phone 7 (or 7.5) projects with VS12. This project type is not supported.
The above is valid if you are on Windows 7. If you are however on Windows 8, then VS12 is sufficient as it allows you to work on Windows Store apps as well as Windows Phone apps (both 7.5 and 8).