Over the past 16 years, I have been involved in 5 successful startup companies ranging from an energy company, to several .com companies. Now I am focusing all of my attention on creating the tipping point in the sustainability movement by pushing initiatives in government, business and the broader social landscape. 
Many people are curious, what I am doing since I left Powerset. Well, the short story is that I have decided to dedicate myself to what I call the new Green Economy and I am working on several initiatives with other leaders in government and businesses that all fall under the responsibility of non-profit that I am founding called SF Green. 
Yes, GreenMountain's BeGreenNow combines the best carbon reduction plan I've seen with the ability to directly buy carbon offsets where you just can't cut the carbon.
I must say, I have seen a lot of carbon calculators (who knows which one is the best) and I have seen a lot of sites that give you advice on how to go Green. But what I always wanted was a website where I could create an account, get great advice, measure my carbon emissions, track my progress toward reducing my emissions and then buy carbon offsets for the rest. If that's what your interested in then you should go to BeGreenNow.
I think the next step in this evolution is to have a badge widget that everyone puts on their website, blog, facebook or myspace account that announces their current carbon footprint and how much carbon they have lost in the past year.