Today, it will silently guess at what I want, and rewrite the query. If they have indexed pages that contain the words I put in, but don't meet their freshness/recency/goodness criteria, they will return OTHER pages with content that contains vaguely related words. "Oh, he couldn't have meant that, it's from 6 months ago, and it's niche!"
They'll even show this off by bolding the words I didn't want to search for.
So, if I'm looking for something that isn't popular -- duckduckgo it is. It doesn't do this kind of rewriting, so my queries still work.