I've seen quite a few posts about AdSense reporting problems and declines in revenue. I don't know about you, but I'm seeing quite a decline in AdSense server response times in the last week or two, and it's getting worses.
Two of the biggest culprits are Invite Media, which is now owned by Google, and Double Verify. Both have server calls that sometimes delay the display of ads as much as 30 seconds or more. By that time, people will click on stop or exit the page.
That doesn't help revenue, either.