It was a match made in geek heaven. Combine the hottest online activity--social networking--with the biggest environmental challenge--energy conservation--and you get something yummier than peanut butter and chocolate. It's not just a mashup of buzzwords, either. Most of us pat ourselves on the back about our energy-saving ways. Sure, we have our vices, but doesn't our routine greenness make up for the occasional slippage, be it bright kitchen lights or an extra degree on the thermostat? Only by talking to neighbors and friends might we discover we aren't so virtuous after all.

That's what social networks could be good for. People's competitive instincts might well be the country's biggest energy source. Also, there's so much confusing and conflicting information out there that it would help to be able to share our experiences of what works and what doesn't. In the past couple of years, a number of sites sprouted up to meet this demand.