I heard that one can only put Adsense ads (from one account) on up to 200 websites, it that true? If it is the case, then what will happen if once put the ad on the 201st site? Thanks Richard
You are thinking of the Competitive Ad Filter. The amount of Adsense ads is unlimited --> # of times you can use your Adsense publishers code.
As Fka200 told you, you are probably talking about the Competitive Ad Filter where you can place a maximum of 200urls that you want to block, and not display ads on your site. Even so, placing your adsense code on 200+ sites can be risky, imagine the risk of click fraud on so many sites...