Atomic - 5:10 pm on May 13, 2011 (gmt 0)
@JoePublisher - thanks for the clarification. I removed the code before I noticed the increase in AdSense impressions. Looking back, yep, each visitor appears to have refreshed the page as many as 9 times before giving up.
I also found this fix, which has fixed the problem for me:
Put this right before </body>
<!-- Correct fb_xd_fragment Bug Start -->
<!-- Correct fb_xd_fragment Bug End -->