Thanks for helping out!
I did ask one of the ad networks, and their answer (just liked I'd expect) was that their ads aren't served locally via my site obviously so my plugin can't cache them. I tend to believe that, b/c these are major ad networks and I doubt I'm the only one using W3C with an ad network.
Might have not been clear on this earlier, but everything was totally normal when APC page caching was selected, just disk enhanced somehow reduces ad impressions considerably. So I assume this has nothing to do with how they count visitors.
Another guess: maybe disk enhanced page caching changes they way the different pieces on my site are pulled in and "de-prioritizes" the javascript ad tags so the site loads quickly but not all of the ad tags are fully loaded before a user is onto the next page?
Thanks again!
