I've just picked up a cheap plug-in power meter (on special for £6.99 at Aldi this week) and can now see that my particular setup is pulling an average of 305W out of the wall socket when the PC is in a fairly idle state. By inputting your cost/kilowatt hour, the meter calculates your running costs at any one particular socket (all your kit is plugged into a single socket via a surge protected extension strip,right?)
I'm on the Click Energy 3 tariff with British Gas which means my Tier 2 electricity costs 8.706p per Kwh so I guess an hour of joy on my PC sets me back 2.66p. Not a bad price to pay for entertainment these days. Yes, I can do deluded so well. The credit card bill for the My System spendfest at Scan hasn't hit the doormat yet. And then I also splurged on a YSP-1100 Yamaha Sound Projector in a separate moment of madness. Oh the pain!