There's a new website that helps you work out how much planetary impact you make. It's at Earthday.net.

Despite being a smug vegan, not owning a car, using public transportation and walking a lot, eating organic food, I am still using three and a half planets and racking up an amazing 15 acres for my comfort and pleasure. I'm feeling more virtuous than Erin at 29 acres (who wouldn't?!) but I'm a polluting wretch compared with Laura, who managed a mere 9 acres and Jason a puny 8, while Olivia consumed half as much (12) as the average American (24 acres).

I have to do some serious carbon-offsetting!