Rasberry Pi vs old Dell, P4
A random smattering of Raspberry Pi vs an Old Dell P4 machine.
Unfortunately I labeled the Rasberry Pi, Debian (it is running the debian image, at least). You can view the full results at OpenBenchmarking.org. Most people are not buying a Raspberry Pi for the performance :), but it is nice to know just how much slower the Pi is.
The dell can pull between 70 - 120+ Watts, while the raspberry pi can pull 5. Unfortunately, in performance per watt, I think the P4 still comes in first most of the time. (The total test time on the P4 was less than an hour, the Pi I left overnight). I didn't do much graphics testing, but the Raspberry Pi chip is physically better (not sure if it's being properly leveraged though).