What I've done...
1) Create ZFS Array, leave settings alone
2) Create ZFS Pool for user share usage - change permissions to Owner (no checkboxes), Group (all checkboxes), Other (no checkboxes)
3) Create users, make them members of the Wheel group
4) Configure CIFS service - name the system, workgroup, make sure Async IO is on both directions, large file support. Don't bother with changing anonymous user/group settings. Make sure the authentication mode is Local User
5) Turn on CIFS service
6) Create Windows Share - name it and associate with the ZFS Pool. I don't think there is anything special set here.
On your windows system, map a drive to the share created in step 6. Try creating a new folder - if successful, then check the permissions, you should see something about your username being one of the assigned permissions, but it'll have the FreeNAS computer name (spec'd during step 4) in computer\username format. All permissions will show as "special"
Now, is this right/perfect, heck if I know - but it works for me! :)