What's funny is how quickly you can get used to not having privacy. Where I work, we have no expectation of privacy whatsoever. Electronic communications in every form are assumed to be recorded. If you would not feel comfortable having something plastered all over the walls, then your don't say it. This puts a limit on your ability to express yourself freely. This may be ok for work, but its really not acceptable otherwise.
We use google and trust them with our search terms and with knowing which links we chose to click on, and how long we stayed at each site. We assume that they will use this in good faith to make money. It seems like a reasonable trade until you realize how heavily your are tracked. Some of these companies probably know far more about our browsing habits, our likes and dislikes that we do ourselves. Further, they have access to this very personal information, and we don't.
They can make predictions about our future purchasing decisions by analysing our usage data. If a company sees that I've visited 5 different websites to research laptops in the last 2 days, there's a good chance that throwing a laptop ad my way will result in a hit and possibly a purchase. Based on other pages that I perused, they might be able to match a specific machine and style to my preferences. If they see that I've also been looking for quotes on luxury items, then the might hit me with an ad that focuses more on style than price - saving the price slashing ads for those who visit sites like walmart.com or who download certain types of music that statistically correlate more strongly with those who are less affluent.
What's really creepy is the thought that this information could very easily be sold to other companies and advertisers without making any attempt to respect my privacy. Do I want my browsing history to be a factor when my next potential employer does a background check on me? Could it prevent me from getting a job, a credit card, or entrance into a school? Some of the damage done by harvesting and exploiting such information might be suffered but never detected.