It's not all that useful if you don't have iOS or Android. They need a way to track your location + I think they scan your mail locally on the device instead of on the server (and they can't do this on desktop).
Yeah, I'm mostly just complaining about their holy war against WP, I was kinda looking forward to trying out Google Now for myself, so it was something of a let down to learn Google still had a personal vendetta against me :P
