and it would be a very interesting project to do some hash/power comparison between desktop CPU & GPU mining vs arm CPU's... arm boards are starting to come down in pricing for what you are getting.
Case in point, I just recently bought one of these:
Odroid U3For $65 you get a quad core 1.7GHz Cortex A-9 with a quad Mali 400... at that price point you can really start doing some interesting things when you look at the hardware costs. Take that to an extreme and put together a
Beowulf Cluster and you could really have a low energy mining machine.