A rectangular Google Ad unit [336×280 or 300×250] normally displays 4-5 different ads but now they are experimenting with a new format that shows 20 different ads in the same unit. It’s done in AJAX.

Here’s a screencast video of the new Google Adsense Ad with scroller button that I spotted here.

Related: AdSense Ads with Live Prices, Contextual AdSense Referrals