Google drives me absolutely nuts because of it's 'intelligence', if you will. With dumber search engines it is trivial to ban words you would only expect to see on pages unrelated to your search phrase, using '-' or something similar. Similarly, if there is a word I know is associated with another topic, but is unlikely to appear in another topic, it's easy enough to force it to appear using '+'.

Google's methods for detecting clustering, or whatever they are using, are so 'clever' I feel like I'm unable to communicate what I want. I feel like I'm arguing with a particularly intelligent and malicious toddler sometimes.

Say I was to ask a toddler to bring me a beer, and they brought me a root beer. I'd be like, "no, bring me a beer, -root."

A normal child would bring me a normal beer, cause that's the only thing in the fridge that has beer in the title without root. The Google child would bring me some sassafras, because sassafras is a root beer, which is a beer, but it doesn't have root in the name.

Annoyed, I turn off safe search, and I say "Bring me a beer, -root -sassafras -sarsaparilla -ginger -cider."

The Google child comes back and says "I couldn't find what you were looking for." I get up off the couch, look in the fridge, and lo and behold it's completely full of beer.