I'm guilty, but, I admit, there are still things I am curious about that I don't know, because, unfortunately, we weren't taught ALL grammar rules in school. Maybe some of that's saved for college??? So I'm not exact, really, no doubt. Just have always been a spelling and grammar freak.
I don't know anyone who uses perfect grammar all the time, especially when speaking. Most people say "gonna" instead of "going to," for instance. However, I do use good grammar all the time in that my sentence subjects agree with their verbs and I never, ever say "me and my friends" or other things like that. It sets my teeth on edge when I hear other people use bad grammar.
Working in radio, and writing news copy, I try to have a vast array of vocabulary and words to choose from. Mostly when writing or reading the news copy, though. And I usually catch myself trying to use proper grammar when speaking, even in casual situations.