It turns out, you can turn those ads off if you want: just go to Settings—Web Clips and un-check the "Show my web clips above the Inbox" box.
Unfortunately, that turns off all the web clips. I do enjoy seeing the quote of the day or links to various news stories I might have missed. And it turns out, on that same page, you can customize your web clip sources. You can't remove the sponsor links, but if you don't care about sports, for example, you can remove the ESPN.com web clips.
You can also add web clip sources from a predefined list of content, or you can add any RSS feed. So while you may still see repetitive and poorly-targeted sponsor links, at least you can make the rest of the web clips show you something that you are interested in seeing.