Even as an ardent Apple product user, I have to admit that the entire prospect of Google Now sounds appealing. Your phone, finally sending you help -- not you asking for it. Push, not pull. Siri can't do that.
I imagine millions will opt-in, and Google Now will drive Android to new levels of success. It's futuristic, easy and cool. If you already use Google Search and other Google products, you don't have to do anything new for Google Now to work for you. Just say yes. Apple will be seen as behind the curve, even as we give more security away, with inevitable and massive personal data breaches and data dumps.
On that note: having already been involved in outrageous hacking plots, I sign into Google as rarely as possible for the simple reason that I don't want my internet habits tracked, and therefore couldn't use Google Now to its fullest potential. I use DuckDuckGo for search, and I opt for other paid products as often as possible (SmugMug, Evernote, etc). I want my money -- not advertising sold against my info -- to be the source of a company's revenue.
I want to be the customer. I don't want to be the product.