Understandably, internet users and privacy watchdogs are up in arms about the move. Gizmodo's Mat Honan explains what the change will mean for Google users (i.e., pretty much everyone), and why it's dangerous:
What this means for you is that data from the things you search for, the emails you send, the places you look up on Google Maps, the videos you watch in YouTube, the discussions you have on Google+ will all be collected in one place. It seems like it will particularly affect Android users, whose real-time location (if they are Latitude users), Google Wallet data and much more will be up for grabs. And if you have signed up for Google+, odds are the company even knows your real name, as it still places hurdles in front of using a pseudonym (although it no longer explicitly requires users to go by their real names).
All of that data history will now be explicitly cross-referenced. Although it refers to providing users a better experience (read: more highly tailored results), presumably it is so that Google can deliver more highly targeted ads. (There has, incidentally, never been a better time to familiarize yourself with Google's Ad Preferences.)....
To read more about Google's new policy, and how it could affect you, read the Washington Post's FAQ.