I have had a chance to do some power draw monitoring of my Raspberry Pi and to compare with other low power ARM devices devices such as the SheevaPlug. The Raspberry Pi is really hard to beat – pulling roughly 2.0w when idle (with nothing plugged in to the USB or A/V outputs) to 3.2-3.3w at load (with HDMI output and USB keyboard and mouse) when using a standard Amazon Kindle charger as the power source. Something I’ve not had a moment to try is decoding HD video as I’d imagine that would load both the CPU and GPU but I can’t see the load being much higher given the combined CPU and GPU part (I’ll update this post when I confirm this).
Contrast these figures against 4.0w idle to 4.9-5.2w load for the SheevaPlug (also without any USB attachments). Admittedly the SheevaPlug has a slightly faster (1.2Ghz vs 700Mhz) ARM processor than the Raspberry Pi, but it also lacks the RCA/HDMI video output circuitry and has a wonky integrated PSU.
Probably the biggest difference between power consumption of the two devices will be related to power supply efficiency. As I already mentioned, the SheevaPlugs are renowned for being let down by cheap and inadequate integrated power supplies. In fact, I’m on my second Plug for that very reason. Since there is no (easy) way to test both devices with the same power supply, any comparison should probably be taken with a grain of salt.