After years Microsoft has changed their mind on this feature. As of Visual Studio 2013 Update 3 RC, an option has been added in Tools -> Options to change to Mixed Case for Menu titles. Obviously this is not for VS 2012 but going forward this option will be there.

Here is the notification from Brian Harry of Microsoft....

Mixed Case Menus – I know I’m going to get some feedback on this one :) This is a long standing request by a vocal portion of the VS user base since VS 2012 to change the “ALL CAPS” menus. In VS 2013 Update 3, we have added a Tools –> Options setting to control whether you see ALL CAPS or Mixed Case. The default is still ALL CAPS but, if you change it, it will persist across upgrades and will roam across your IDE instances using the VS Online roaming settings feature (if you log into VS so it knows who you are).

http://blogs.msdn.com/b/bharry/archive/2014/07/02/vs-tfs-2013-3-update-3-rc.aspx

After years Microsoft has changed their mind on this feature. As of Visual Studio 2013 Update 3 RC, an option has been added to change between mixed case and upper case: Tools -> Options -> Environment -> General -> Turn off upper case in the menu bar
Obviously this is not for VS 2012 but going forward this option will be there.

Here is the notification from Brian Harry of Microsoft:

Mixed Case Menus – I know I’m going to get some feedback on this one :) This is a long standing request by a vocal portion of the VS user base since VS 2012 to change the “ALL CAPS” menus. In VS 2013 Update 3, we have added a Tools –> Options setting to control whether you see ALL CAPS or Mixed Case. The default is still ALL CAPS but, if you change it, it will persist across upgrades and will roam across your IDE instances using the VS Online roaming settings feature (if you log into VS so it knows who you are).