I checked my quantcast stats a few weeks back after taking off their js months ago. I noticed that they still had a good picture of views/etc and wondered why. It appears that they were getting info from Intense Debate.

I originally took the Quantcast code off my site b/c it slowed things down and despite having fairly accurate counts, it had skewed demographics. I didn't want to encourage them, so I took off the script. However, my use of IntenseDebate meant that I was still using it.

I don't think IntenseDebate is doing anything wrong, but I would like an opt-out.