Id do it if I were responsible for that person's work. Not sure that Id do it in a conversation - like say someone used a word incorrectly. I probably wouldnt say anything. But in print, if I have to sign off or appove, then hell yeah. People often ask me to proof read or edit their stuff b/c I have a good eye for it I suppose.
I do correct my son when he uses incorrect grammar but I dont do it in a critical way. I just repeat the proper word or usage right after he makes the mistake. So if he says "I swimmed at the pool yesterday" Then I simply say "swam". And he says "YEAH, SWAM". And we keep talking.