Google AdSense programme policies allow you to place up to three ad units and three link units on any page. Is that saying your aloud 3 of each on a site? Or just 3 in total? Cheers
3 ad units on each page only however if you try to do otherwise i dont think there is a problem if they dont catch you. look at the my digital life website to see what I meen
Always remember 3 is the maximum in a web page but you can have lots more if you have lots of webpages.