Those are the big three. On the whole, I think I'm pretty consistently good at spelling. But with those three words, I'm so aware that I often get them wrong, I second-guess myself into forgetting which spelling I'm trying to avoid. Just typing out the first paragraph here, I checked all three of them against dictionary.com, just to make sure.
Lucky I don't have to take dictation! I'd probably panic if my boss told me to write somthing about how she can't go to a chain, because it's "neccessary to support the independant restaraunts."
Apparently I'm taking hypothetical dictation in a food-service-related industry? Ok.