Using Multiple Ad Blocks

Google lets you place more than one ad unit on each page of your Web site.
In fact, you can place:

3 ad units
3 link units
3 referral units
2 AdSense for search boxes

What does this mean for web publishers?
A real bonanza: you now have many more chances to hook readers with new
ads as Google will show unique ads in each ad unit!

With multiple ad blocks, you can also decide which ads are served in the best
places for your site.