I have "well" and "good" sorted out to the point that it songs wrong to me if they're used incorrectly. I have trouble with "lay" and "lie" though.

If you really want to talk about obscure grammar mistakes: how many people here are aware that the ordinary use of the word "hopefully" is incorrect? I tell people to correct me whenever I use it. One day my terribly, terrible habit will be fixed.

BAD: "Hopefully I will have a lucid dream tonight."
GOOD: "I hope that I will have a lucid dream tonight."

Pointing out grammar mistakes for the intellectual betterment of mankind is a truly excellent thing to do.