Some still view Siri as nothing more than a gimmick, and perhaps two years ago, that might have been a fair assessment. But with the launch of iOS 7, Siri sheds her beta baggage and is more useful than ever. So is Google Now, which Android fans would argue is an even more intelligent assistant. Regardless of which one is better, it's clear that this is becoming an essential part of the mobile experience, and it's Microsoft's turn to implement a personal assistant of its own. Well, meet Cortana.