Google works amazingly well and makes everyone's life easier. But don't think for a minute that they aren't making use of all the data they are compiling on each and everyone of us who utilizes their site, for profit and power.
Everyone seems to trust Google inherently, which I think might be a tad naive. This company has an enormous amount of information which could very well end up in the wrong hands and prove dangerous someday.
I'm hoping that won't happen and trust the company (brilliant I've heard) has put the appropriate safeguards in place.
Google is a great search engine, but also a major privacy concern. They track *everything* you search for and it is tied to each computer or IP address you use. If you use a Google application (such as Google Desktop), they can attach the stored information to your own personal information. While I doubt that Google has any malicious intent, just look to the AOL search info leak to see what kind of embarassment leaked search terms can cause. So, use Google carefully and make sure you clear your cookies (or use an addon like CustomizeGoogle) to minimize the amount of data that Google collects about you.