Power consumption of the Raspberry Pi Model B & B+ & an Arduino Uno R3
A lightly-loaded model B with keyboard = 1.89 W -> daily 45.36 Wh
A lightly-loaded model B+ with keyboard = 1.21 W -> daily 29.04 Wh
B+ with LAN/USB chip off (no i/o except GPIO) = 0.76 W -> daily 18.24 Wh B+ shut down = 0.26 W -> daily 6.24 Wh
The B+ really offers huge improvements in the power circuitry. Wow!
For an Arduino Uno it seems to be around 230 mW at idle, and putting it to sleep helps a bit mut not that much since the USB is still running it seems, so about a 25% saving only.
It seems that a Raspberry pi B+ can compete with an Arduino Uno in idle in terms of power consumption. You've got to get one of the Arduinos without USB to get to the real low power stuff.
How Much Less Power does the Raspberry Pi B+ use than the old model B? » RasPi.TV