RasPi does have a Broadcom ARM Peripherals data sheet that documents BCM2835 GPIOs and serial peripherals connected to RasPi's expansion header. This is enough for most users. The full data sheet is not available, but since you can't buy the BCM2835 in small quantities it wouldn't be that helpful anyway. Some people are upset about this, but it is what it is and there are plenty of alternate boards available, like BeagleBone.
BeagleBone and RasPi address different markets. BeagleBone is targetted at EEs who need lots of I/O pins and serial peripherals, or people who need an integrated Ethernet controller for performance and/or a USB host that's better behaved. RasPi has better video processing, so it's preferable as a media center. The price difference between RasPi Model B (plus an SD card) and BeagleBone Black is minimal.
I have had several professors tell me they refuse to use RPi because Broadcom will not release a DS for the MCU. Does this bother anyone else? RPi is losing potential adopters to Beagle Bone because of this.
Yup, noticed that after I went back to reread the thread. Further investigation does indeed reveal existing dedicated Bitcoin mining hardware that can far outperform the Parallella, at least in this application. And there are now even USB Bitcoin miners, as noted in the Raspberry Pi tutorial mentioned, which shows how to use the Pi as a headless controller and monitor for these devices. Very interesting.