> "how can Google use this data against me" I look at it the other way: What do I gain from allowing Google to build this profile of me, including information

> "how can Google use this data against me" I look at it the other way: What do I gain from allowing Google to build this profile of me, including information from potentially multiple accounts, devices, location history, search history and communication history. Because if Google is offering their services for free to all comers, that data must be valuable to them. And if I can't deduce why the value is what it is, that's far more likely a failure of understanding on my part than any indication of fairness or harmlessness in the exchange. [1] And to me, all I see is a convenience function I can't rely upon. It can identify flight or meeting information. Maybe (who knows what parser errors exist or will exist as things change). And it can only even try some of the time, as google doesn't have access to every channel by which my itinerary is set and changed (emails to non-Google accounts, phone calls, text messages, verbal communication, etc.) And if I can't rely upon it, I have to double-check that it is operating off the right information. And at that point, I might as well have explicitly handled the bits Google Now might have gotten right as well. The rest of your examples are replaceable with client-side data-detection features -- that have been identifying likely dates, addresses, flights, etc and offering convenience functions to simplify dealing with them for some time -- and location-snapshot information [2]. Nothing there requires indexing all my communications and locations across history. Maybe Google Now can become something that's worth the trade-off. Or maybe Google will offer a (for-pay?) version with guarantees about who has control over what is retained and who has access to it. But, to me, it's not a good deal right now. And besides all that, I'm personally a pretty private person, so I have a particularly good imagination of the downside risks, even beyond weighing my benefits vs google's benefits. [1] It's that old saw: "There's a sucker at every table..." Applied to internet services it suggests: If you can't tell why a company with a free service has a massive valuation and a willingness to pay through the nose for users, you literally have no idea what you're trading away by using it. So you better be damn sure you're at least getting something worth the per-user valuation in return. [2] Yes, it requires some degree of trust or self-deception to believe that there's a difference between a company that states it's collecting your location history and one that claims it doesn't -- as providing snapshots implies the ability to log said snapshots. But such is life. At some point you make peace with the level of paranoia you can handle, or you opt out of society altogether.