I have been noticing ads not appearing with my IE too, although I think my issue is with my firewall purposely not allowing ads for it. Haha, so really that's not much help at all to you.
I've only noticed this if I'm developing a page on my desktop and try to load it locally... if I post the page to one of my sites, it works fine. Were you trying to view yours locally, or published on your website?
Hey you're right, it only happens when viewing my pages locally. Thanks for noticing that. And yeah that would be a good way for ms to mess with google