To save others the angst, I just wanted to report that on the latest Mac OS X (El Capitan 10.11) the Beaglebone Black is currently not usable via the USB connection, except as a storage device. The alternative is to power it somehow and connect via Ethernet.
Normally there are two methods of console connection via USB: as a virtual network device using HoRNDIS or as a virtual serial device using FTDI USB Serial drivers. Both are thwarted by El Capitan because it enforces kext signing, but for slightly different reasons:
If anyone discovers improvements on this state of affairs then please let us know. I'll do the same.
Regards,
Heath