I know it's not the most pleasant feature for users (showing them their contribution to destruction of our planet.) I think it would go a long way in raising self awareness.
I may be missing something, but I had an imported iCal trip last weekend that I can no longer find. My journal says, regarding this trip, "We imported a trip (since deleted) from an external calendar."
This seems like a problem, especially given your super awesome carbon calculator working on the basis of old trips. (I noticed this while trying out the calculator.)
Suggested behavior for trips imported from iCals: Once the trip starts, disconnect it from the iCal so that when it goes into the past and disappears from the iCal, it doesn't disappear from Dopplr.
What would serve as a good comparison for evaluating your carbon?
At the moment Dopplr shows you the raw figures, but we realise without independent research it's tricky to know what that means.
We're chatting with the good folk at http://www.amee.cc who power our calculator about this, but wanted to open up the discussion here...
BTW - a while back I asked what the carbon footprint of freezing Han Solo in Carbonite would be (http://tinyurl.com/6mac24), but I figure we might run into some trouble if we used "Solos" as a unit of comparison... ;-)