In other news, I bought a mains power meter to measure the power and cost of running appliances around the house. To start with, I tested the consumption of our two main computers (my brother's C2D and my i5) and got some interesting results:
i5 760 (2.8GHz, 4 cores), ATI HD 5870
idle: 55-60w (CPU @ 1.2GHz)
4 cores loaded: 120w (CPU @ 2.93GHz)
4 cores + GPU loaded: 270w (CPU @ 2.93GHz)
2 cores + GPU loaded: 250w (CPU @ 2.99-3.05GHz)
C2D E8400 (3.0GHz, 2 cores), Nvidia GTX 470
idle: 80-90w (CPU @ 2.0GHz)
2 cores loaded: 130w (CPU @ 3.0GHz)
2 cores + GPU loaded: 350w (CPU @ 3.0GHz)