A few days ago i began noticing a slew of WordPress 3.3 self pings.
I kept noticing an entry with no referrer "/?attest=true" with my servers IP being recorded every time someone visited the site. After i contacted my web host it was determined WordPress was massively self pinging itself.
I checked everything that could possibly cause a self ping and found nothing. Then started disabling plugins one at a time. As soon as i disabled the social sharing plugin Add This V-2.4.0 the self pinging stopped.
I had recently did an update of this plugin, and had the previous version on disk from a previous backup. Restoring Add This V-2.3.2 cured the problem. I also notified Add This of the ping problem with their plugin, but have not heard back from them yet.
So if you are seeing a slew of /?attest=true entries in your log file or stats that baby is what is causing it. Its a real PITA when developers rush to release updates that are not fully tested!