Go into your VS2010 folder (by default My Documents\Visual Studio 2010) and then go into \Templates\ProjectTemplates\C# copy the "Micro Framework" directory to the same directory in your My Documents\Visual Studio 2012 directory.
You should be then good to go. I'm not 100% sure about the location of the VS2012 'My Documents' directory, since I haven't upgraded mine yet (work requirements) but it's extremely likely that VS2012 doesn't use the same templates directory as VS2010, so you'll have to copy them over manually.
--Me.
I installed the MF 4.3 beta and this steps where the only thing missing to continue making projects with my N+, worked like a charm!
Thanks a lot!
- smurf likes this