I work in written communication, so pronunciation isn't something I have to think about a lot (professionally at least). I didn't really become aware of this until two years ago. I didn't know the correct pronunciation of couture, the fancy catch-all word that is used anything to do with fashion, until I was 23.
Someone at the newspaper I was working at said it, pronouncing it coo-tyoor, and I said, "What's that?" They told me, and I said, oh, you mean coo-cher. I was laughed at. (Webster's New World gives the pronunciations as koo-toor or koo-tyoor, so the laughing was justified.)
I'd never heard it spoken out loud before, and since then, I've always wondered what other words I've been mispronouncing to myself over the years. It doesn't matter that I do it to myself, but I'm bound to have another coo-cher moment in the future.
(I still like coo-cher better, by the way. It's more fun.)