In my main Gmail account I get "WebClips" - which is an ad formatted in one line at the top of each message. I never read them and click on them less often. I rue the day when Google made the change from the "old-style" Gmail ads - three in a box on the right side.
I actually liked those old ads, and clicked them fairly regularly. Google also had "related" content there.
I discovered today that old format still exists when I logged into an alternate Gmail account that I don't use much. Surprise - the old, beloved ad formats!
The obvious upshot - format and positioning can make a big difference on user experience. And if anyone knows how to set a Gmail account to get the old ads, and eliminate the web clips, I'd love to know.