Well, it seems to intermittently affect different people. Note, these ads are served up by googleads/doubleclick, which is going to serve different ads (or at least take different metrics) depending on where you are, and what route you're taking.
But, this problem is definitely manifesting itself to a number of people in exactly the same way, across very different platforms... So I don't think we're all on drugs... I wouldn't even say it's Avery's config neccessarily; I think it's related to the ads, *they* are probably screwed up, and loading 7 layers into a frame.
EDIT:
Yup, that's exactly what's going on. Each one of those frames, that loads the failed ad, actually loads 7 layers into history. Hitting the back button actually executes a 'back' only on that ad frame. The URL changes each time, 7 times, until it finally "runs out" and then the "back" is issued to the entirety of the page itself.
It seems that they are responding with an Error 400; "malformed request", which I'm guessing has something to do with the configuration of the URL itself being served.
Avery, if this is any help, here are some of the URLs that are failing when the ads are being served.
... Seven of those will be loaded, in sequence, one after another, in each ad frame. Because of this, page history becomes 7 layers deep, and is not actuallly backing out until the first in the series is reached.
I'm guessing that this 'broken' ad is being served in some locales, and not others, due to google/doubleclick's "intelligent" network which serves ads based on IPADDR/geolocation crossrefs. ... This is probably why some people aren't experiencing the problem.
Here's what those of us who are having the problem are seeing, (in addition to experiencing the 'must hit back 7 times' phenomenon.) -- This appears to have started to happen 4-5 days ago. Maybe 6.