Some people are worried at the evidence that "someone" out there is watching over our shoulders, whatever we do on the internet, and then targeting our "interests".
"They" know where I am. The info is used in side-column car insurance and mortgage ads which claim to be specific to my state or my town. They are annoying and look painfully obsequious.
I bought a toddler pedal car for Nugget's 2nd birthday (next month) on Amazon. Now every time I turn around, I'm getting ads from toy stores for toddler pedal cars. How many of them do they think I'm likely to buy? They are pissing me off more than attracting me.
Youtube keeps track of what I watch, and then when they make recommendations of what I might like, the list consists mostly of videos I've already watched. That is obviously stupid. They've managed to put together a list I'm pretty much guaranteed NOT to be interested in seeing. (Watch out for the Eastern Europe trap. Once I watched a Russian video, and for the next week all the recommendations were Russian! I didn't even know what they were about!)
EBay likes to take something you bought, then make recommendations of other similar things you might like. That might be useful to your shopping, but the execution is very annoying. You just bought a unique handmade item, and eBay informs you that "Others who bought this [photo of your unique item] also bought this, this, and this [photos of other unique items that are still for sale]." It's obviously a lie! No "others" bought any of those items!
Ok, maybe computers are getting smarter, but programmers are getting stupider. I don't think we need be worried.