I use dictionaries all the time. I use dictionaries when I encounter an English word that I don't know, which is not infrequently, despite BS and MAT degrees. I use dictionaries to check spelling, often built in to software as a "spell check" functionality. Let's consider those as dictionaries too, and also dual-language dictionaries, like Korean-to-English and English-to-Korean. I use those dictionaries constantly, maybe even too much, in studying Korean.
I was thinking about dictionaries today, and I realized that they are really pretty amazing. My thought was probably catalyzed by this Dinosaur Comic
that mentioned Shakespeare was writing just before dictionaries began to be made, which contributes to his influence in shaping English just at the crystallization of the written language. Aren't dictionaries amazing?
Thanks to dictionaries, just about anybody who uses something we can call English can read just about anything written by anybody else in English too. I can read just about any specialist's work by looking up technical terms, even if it's slow going.
But even more generally, thanks to dictionaries, people on opposite sides of the world, who have never met, even spell things in the same way. Some new words and usages that people in Canada or the UK come up with haven't made it into dictionaries yet, and they catch me by surprise sometimes, but by and large people all use words from the dictionary.
Imagine the past, when people in your village would probably talk almost exclusively with family/village members. Even just twenty miles apart, it could become difficult to communicate in short order. Of course the older generations would still exert some stabilizing force on the language, but I don't see it as matching modern conditions.
Of course language still changes - there are some expressions unique to my family, even now - but I can't help but think that it must be changing a lot less than it used to. There are so many homogenizing forces, like dictionaries. As much as some people say dictionaries are only records of usage, the prescribe as well, and many people consider the dictionary spelling and definitions "correct". The dictionary has a prescriptive effect.
I think education must have a similar prescriptive effect, and I would guess that especially since the spread of required and/or public education, the rate of change of language overall has declined.
It's anecdotal and possibly stereotypical, but if you think about where new "slang" comes from, it's generally the less-educated rungs of society.
There's also urbandictionary.com of course. I go there sometimes to find out what the heck people are talking about. Every once in a while I need to find out some internet neologism, but I used it far more often when I was living and teaching in New York city...
Anyway, my impression is that because of dictionaries, standardized education, and widespread publishing and broadcasting, languages are probably changing more slowly than they used to. But I could be totally wrong. It makes me want to ask a linguist. A linguist who specializes in this kind of thing.
(added later) forgot to note: original idea was also about dictionaries being BIGGER than any individual's language/vocabulary...