With a Group Account, how can a user view what permissions he has on shared folders? How does the user know if he can write or read-only for a particular folder? Conversley, as administrator, how can I see the permissions I've set for my folders and what users I've set them for and how can I look at a user and see what permissions he has?

The user can only know based on what toolbar buttons are available to her.  The administrator will know by going to the manage share screen.  If they double click on a share, the permission level will be displayed.