I'd agree with that, pleeker. If you think of it as AdSense for email, that helps to clear up some of the confusion. In the same way that AdSense targets an ad based solely on the content of a page, the ads in Gmail are based on the content of that one email.
Fair enough, GG, and it's a valid comparison. But make sure your PR guys (other than you!) realize that everyone uses email ... and very few (comparatively) use or have even heard of AdSense. It's got to be put in terms that Gmail users, and the public in general, will understand.