Coke Zero is definitely Coke's equivalent of Pepsi Max. They are aiming it at a demographic of young, vibrant people who don't like the idea of buying a 'diet' drink. The drink itself, according to Americans, is truer to the taste of Coca-Cola classic - in other words full fat coke without the calories! Many Americans find Diet-Coke isn't sweet enough but Coke Zero has changed all that by using aspartime and something called acesulfame potassium, essentially making it much sweeter than Diet Coke (funnily enough many Americans who dislike Diet-Coke find Coke-Light better because it is slightly sweeter).
Anyway, Coke Zero has been hugely succesful in various countries, especially Australia where it has been aimed at men and tied in with Aussie Rules Footy and Rugby League. They have suffered in Australian soft drinks market recently but the arrival of Coke Zero and the clever marketing of it, has increased sales by 19% in the first 6 weeks.
Depending on the marketing over here, I think Coke Zero will be pretty succesful. It's a Diet drink that's marketed as a cool, action drink - something the lads can share. I think Coke feel that with Diet Coke being so succesful, it will continue to be bought by women, whereas Coke Zero is very much aimed at the boys!