I stumbled on 'the carbon account' today via Peter Armstrong's blog and I was pretty impressed. It's a new personal carbon usage calculator that goes into lots of detail about every aspect of your energy usage and gives you a pretty decent representation of your carbon footprint.
The thing I love about this site is that it actually goes to the trouble of finding out how electricity is created by the company you use, and also finds out data about the vehicle you drive rather than just giving you an arbitrary average.
Unfortunately its only available for UK residents at the moment, but if you happen to live there have a go and see if your carbon footprint is as small as you think it is and how it compares to your friends. Post a quick comment to this blog with the results too so we can get an idea of the average carbon footprint of NI readers. :)