Adding "Application Data" on the end of a file path is never a good idea for the same reading that you should not add "My Documents" on the end, as it may not be called that in a version of Windows with a language other than English. It may also change in the future (they changed between XP and Vista remember).
Also ALLUSERSPROFILE is only meant to point to the root of the All Users folder and has nothing to do with application data. That's why COMMON_APPDATA returns a path that includes the Application Data folder.
I'm not sure I want to be storing files in a hidden folder anyway. My next game will have a level editor and it wouldn't be good storing them in a hidden folder, because the user may want to email them to their friends. Then again, it's not ideal sticking them in the Program Files folder either. But that's another issue altogether, which I'll deal with when the time comes.
Also ALLUSERSPROFILE is only meant to point to the root of the All Users folder and has nothing to do with application data. That's why COMMON_APPDATA returns a path that includes the Application Data folder.
I'm not sure I want to be storing files in a hidden folder anyway. My next game will have a level editor and it wouldn't be good storing them in a hidden folder, because the user may want to email them to their friends. Then again, it's not ideal sticking them in the Program Files folder either. But that's another issue altogether, which I'll deal with when the time comes.