It's not unusual for other search engines like Yahoo, Bing or Ask to advertise on Google. But I've never seen Google run an ad on another search engine until now.

I did a search this evening on Bing for Google Chrome. To my surprise, there was an ad right at the top of the page advertising Chrome, apparently from Google:

What's that big box below the ad? That's Bing doing a special "Best Match" unit. It's completely editorial and not connected w