I can't help that my mind naturally and automatically notices spelling errors, but I can certainly decide what to do with the observations when I have them. There are times when it's clearly right to point them out, like when someone asks you to look over something they wrote. And there are clearly times when it's wrong, like when they're just chatting. (Occasionally, you can point them out then in the form of making a pun, but you have to be careful.)
The in-between times are surprisingly common for me, though. There are any number of places where a person has written some kind of text that is going to be seen repeatedly and indefinitely, but where a spelling error doesn't really matter, per se. For instance, the signature appended to someone's emails or forum posts is going to be used over and over, so it makes sense it should be right; but if it's wrong, it's not like you're going to make a bad impression with a potential employer or someone else who it really matters to impress. How about the message your instant-messenger shows when you're away from the computer? If something's wrong, most people won't notice and most who notice won't care, but does that start to shift when you've had the same spelling error in it for a year?
In these kinds of cases, I think if the person himself (or herself) noticed the error, he might want to fix it, might even be very mildly embarassed by it. But there's no way to draw their attention to it that might not come off as critical or even insulting. Yet the error keeps jumping out at me, over and over. I can't tune it out.
This must be how Siobhan is with sounds.