it's not just health. look at Google Now on android 4.1. they're going to know everywhere you went and a lot more info. sooner or later, this will likely lead to targeted ads if they can deliver high-value ads the user actually wants. ie., [you're driving past your favorite pizza shop] Pizza Boy is offering $5 off today your normal order. Should i place the order for you?" the reason most everyone will opt in is because of the high value-add it provides. my wife quickly opted in to Google Now on her android phone cause she wants the extra features.