In this HowTo at http://forums.linuxmint.com/viewtopic.php?f=42&t=69834, Method 2 with bindfs will produce a shared directory into which users can move files/folders from their own home directories into the shared directory, and those will be writable by all users.
But Method 1 with Linux permissions will not support the same functionality, will it? As far as I know, even with SetGID and umask=002, files moved into the shared folder will retain their original group rather than the SetGID group, and thus will not be writable by other users.
And as far as I know, even adding ACLs to the recipe cannot overcome this problem -- though I'd be happy to be proven wrong!
Confirmations/denials/improved Linux-permissions recipe?