For figure skating, I would put the percentage of high-end participants (top 10 in each major country) at 2% (assuming you don't consider rhinestones to be doping).
For the Tour de France, I would put the percentage of participants in the 2010 race who are doping at 90%. The other 10% wanted to dope but couldn't get their shipment of testosterone patches through customs. I mean, it doesn't do much good to have just Armstrong doping. I assume his posse can't do him any good if they are at the bottom of the mountain sucking on oxygen tanks.
That's what I think.
-- Random Error Generator, Version 4.0
-- Master Moonballer