I am not paid to fly and purely fly for fun.
I'll fly as often as I can afford, because I can see the future of GA (not commercial but private) as short - through taxation & over-regulation under many guises.
It frustrates me that my costs increase while services decrease and I am pretty sure that the net effect of Copenhagen / Carbon Trading, etc., will be increased taxes for 'Ordinary Joes', with little or no evidencial proof over time that our 'positive actions' have had any retarding effect - the result will be '...we must do more!'...pay more tax...no result again...do even more...pay more tax...no result again...etc.
Minor rant over.
As to carbon footprint, I turn my lights off (not landing light) and the heating down, plan my routes (road and air) efficiently and walk to the pub.