Personally, I'm going to use one of them for a sort of NAS box for my backups. The only network access will be via SSH, with key access only, and a "command=" target in the authorized_keys file so that it you can only backup to it and restore files from it -- but not destroy data. Always nice to have a dedicated backup server in case your system gets hacked.

I was going to use a RasPi, but I/O was too slow as it had to shove both the Ethernet and Disk through the same USB controller.

The other thing I'm using these things for (at least the RasPis) is a temporary fix for when someone's computer is busted -- it gets them back online with access to most of their daily routine, while I'm taking time to repair the PC. The BBB might have a bit more performance, so I might add that to the mix too.