I can't find it now but a few months ago UCI's doping probability rankings were leaked and published in a magazine. I'm pretty sure there was a link on here which is how I found it. It scored them all from 0-10 depending on how suspicious their test results were.
From memory, I think Lance was a 7 and Schleck and Contador were 5 and 6. Cavendish may have been a 3 or a 4. Only people who were <2 were considered 'probably clean'
Does anyone have the link? It was the most interesting thing I'd seen by way of an answer to the question.