Greg,
I would rather both units sync when turned on so that when I back up my waypoints to my PC, I don't have to back up from both individual units then have two separate backups to my PC. Also if one of my units goes down, I will not have the waypoints marked on the other unit. I recently sold my Interlink and purchased Ethernet with a hub so that I can connect 3 units, to my dismay I the Ethernet hub does not store all the data on the network! For $200 which is simply a weather resistant ethernet hub, I would expect some more intelligance and memory storage.