Privacy on any Google site is non-existent.
They keep all your searches forever.
It has been shown that they release data to 3rd parties, which is supposed to be anonymised, but the other company was still able to find the person based on their search history.
Example: if you only use Google as your search engine, then every site you visit will be found by google search (or 99% of them). If you have a child for example, you might google to find your local PTA group at the child's school, you may search for shops in your area, you might want to look up a gym in your area, et, etc, etc.
If I had all this information about you, I am pretty sure that sooner or later I would find you, or your children's school, maybe even your name and address (you have googled your own name before, right? AND you probably entered your address to look for something nearby).
Now remember, ALL Google services are linked and share information between each other, tracking you by various means, and this information is stored FOREVER. Maybe worst of all is if you use Google Maps, Google Earth or use the Google search from a mobile phone - they will know where you are IN REAL TIME based on your cell/mobile phone location. If the phone has a GPS built in they will know where you are the whole time the phone is on (on Android Phones - Android is a Google operating system for phones).
Even if you are not doing anything illegal, or immoral, do you really trust a company with such a terrible privacy reputation and history ?
Ask yourself this, would you be comfortable your neighbour having all this information about you, or your EX, or your children, or your parents?
If the answer is NO, then why on earth are you trusting this information to a corporate giant who keeps it forever, never deletes ANYTHING you type into any of it's hundreds of services. So maybe your information is "secure" for now, but companies buy and sell each other ALL THE TIME (including their databases, etc). In 5-10 years time, it may be owned by Microsoft, or BMW, or most likely a company who will want to buy Google for the information it holds, and they may not just keep it - they might actually use it to do some pretty nasty things with it.
Why on earth you would STILL use Google search, when Microsoft Bing search is available (with pretty much the same results and more of them usually).
You already "trust" Microsoft if you use Windows, and so far they have done nothing to break the privacy trust, and they have been around since the early 1980s.
Google is the "in" thing now, but when they are scrapped for cash, I BET YOU MY BOTTOM DOLLAR THEY WILL SELL EVERYTHING THEY HAVE TO MAKE A DOLLAR.
At least that's the risk we are taking using Google Search, they have been on the block for what? 5-10 years (when they became really mainstream).
When you fall in love with someone, you never find out their DEEPEST DARKEST SECRETS untill several years into the relationship. Microsoft has proven that privacy wise they are so much better than Google over the 30 years they have been in business.
Google, I think people are still in the first stages of romance with it, but they don't know who Google is, how it thinks and operates, and it's DEEPEST DARKEST SECRETS are yet to show up.
This is an official web site of Google.
For years, they have promised countless times they would never combine the data they gathered about you via all their services. But now, with the weak excuse they had "no other choice", they are going to combine all the data including your IP address, cookies, search terms, e-mails, social activities, location and whatever-the-**** you even didn't know yourself they know about you into an ultra-personalized profile. (As of March 12, 2012.)
They will now know who you are (profiles, Gmail etc.), what you do (docs, maps, Android phone), what you buy (checkout / wallet), what websites you visit (Google Analytics, present at many of the most popular web sites), who your friends are (Gmail, Google+), what you watch (YouTube)... You name it. They will use this info to serve you super-targeted ads. Only DoubleClick advertising (for 3rd-party web sites) isn't included in the list of services for which they are going to combine info. At least, for now...