I absolutely love my beaglebone, aside from some issues with the Linux drivers for the USB host port, it's been very reliable and useful.
To date, I've used my beaglebone to
- stream live video of my baby kittens from the window well they were born in outdoors (their mom was a feral cat, I used the video stream to keep track of them until they could be rescued and brought inside)
- transparently encrypt USB drives using the client+host ports [1]
- use the onboard hardware RNG and some custom python[2] to supply entropy to other boxes on the local network
- use it as an offline environment to perform sensitive PGP and CA signing operations
And I'm toying with the idea of building some kind of open source network/USB connected hardware security module system with the BeagleBone as the reference platform to run it on.