As a non-native speaker, I'd love if I were corrected all the time! These little mistakes are prone to getting stuck in your head and hard to get rid of if uncorrected (especially since the Internet is filled with non-native speakers making the same mistakes over and over again).

Curiously enough, I hesitate doing so myself when I notice a mistake, in case I bother or embarrass the guy. I think I'll start changing that :P