The main problems are to do with sharing data across accounts. If you are attempting to write to a shared file (in the shared directory) and you did not create it (in your account) then Vista will block access. However this is only a permissions issue and setting the file permissions to "everyone" will resolve that issue. The same with virtualised directories, virtualisation is done on a per user account basis so whilst your game may well be available to the "installer" it may not function for any other users on that machine.