Nothing has changed in terms of tracking because things such as location, calendar, check-ins, etc. were already beeing tracked and the things that Google Now shows as inferred (you will be late for your work due to traffic, let me reroute, etc) are already possible and certainly affecting the personalized advertizing (you support team X, how about this sports jersey). The only difference is that now this a stand-alone product that wraps such insights into something that is more tangible and more valuable to the end-user and hence makes it, as article's author points out himself, much more lucrative reason to share your personal details such as the above-mentioned.