anyone know of any good resources, tutorials, books, etc. for putting the PRUs to good use? those seem to be the defining feature that separates the BBB from the other SBCs.
I can recommend "Exploring BeagleBone" by Derek Malloy which offers a very gentle introduction to the PRU with some mildly advanced examples.
Also, a shameless plug with more PRU code examples in case you are interested to use Rust rather than C for the glue code:
https://github.com/sbarral/prusst