The internet has come a long way in the past 20 years. From the basic days of a text based web on graphics far from HD, we're now in the time where every errant Google search stalks you through every corner of the web. Everyone has that family member with a weird hobby or interest. Because you love them, you chose to indulge them on their birthday. You went to amazon.com and started searching for all sorts of eccentricities before settling on a gift, piece of cake. The only problem being... now every site you go to is covered in ads for horse head masks, bloody shower curtains, and bike helmets with mohawks on them.
That's no coincidence, that's targeted advertising at work. Were you enticed to click on any of those ads? Doubtful. It's definitely noticeable though because you'd never search for anything nefarious otherwise... right? Am I right? The fact is, it's happening a lot more than you realize every day. You probably just don't notice the other targeted ads so much. The most likely reason being that they are more closely aligned with your interests.
I wouldn't be surprised to regularly see ads about the Texas Longhorns, as I frequent lots of sites and media related to the Longhorns. When I do make that one-off search for the Aggies, and then start seeing ads for Aggie stuff, it's a lot easier to pick those out of the bunch as related to that one particular search.
There's a fine line to be walked by advertisers between ads targeted effectively towards their audience and a disaster scenario of a very ineffective and potentially creepy or badly timed ad turning away potential customers before they need your product to begin with. In the Time link below, you'll read where maternity ads gave away pregnancy secrets. In another case, ads for engagement rings gave away the element of surprise for a guy asking his lady's hand in marriage. The Slate article mentions a woman who shopped for underwear at home, then the next day at work choice in underwear styles was revealed through targeted ads while screen sharing with co-workers. Is this just a fact of life in the digital age? Does it have to be this way?
For the most part, targeted advertising is an unobtrusive fact of modern life. You can, however, game the system beforehand to prevent these ads unaligned with your interests from following you around. Your first option is the Private Browsing or Incognito mode in your browser of choice. Simply open a new private window, do the searching you don't want following you around, then close the window. That quick browse isn't tied to the same profile as your normal browsing, and you'll not get stuck with those ads. A second, more long-term option is to install AdBlockPlus's browser extension. This is a bit more extreme of an option, and will prevent a lot of ads from showing in the first place.