Use CSIDL_COMMON_DOCUMENTS
That solution has been floating around in my head for a few weeks now, but its off putting as you mentioned because portals or users may not like it.
So I was floating around with the idea of creating a hidden directory in there that contained all the game info that I need to share amonst users...
If its hidden, it'll not get in anyones way, so there really shouldnt be a problem.
Dabz