I have a web site thats about a month old and one of the pages had about 12 h2 tags. Everytime I refreshed the page, I would always get the public service ads. I thought I had too many keywords in the content and started removing and re-writing the content, but made no difference. The next step was to remove 6 of the H2 tags and now the regular AdSense ads show up. I then put the H2 tags back, and the public service ads came back. I would like to add the text for the H2 tags were related keywords to the main keywords. Sure was strange and consistent.
since they can be formatted in css, maybe he just used them arbirtarily, as opposed to the smaller h4s, or whatever. I find myself using 4-8 h2s quite often. I didn't know that was bad, I thought it was quite the opposite.
Not exactly bad, but Compar has an interesting opinion about that over here http://forums.digitalpoint.com/showthread.php?t=1548