I usually email them the correction...

I sure agree that informing people privately is - in some cases - a good way to handle this. It's just that I feel that /msg-ing people for every minor glitch is just a tad too much fuss for my personal taste. This applies to both sides: it usually takes me more than a negligible amount of time to find a wording/tone that I'm happy with, and they in turn might feel obliged to send a thank you, etc.   YMMV, of course... maybe I'm just a bit lazy at times :)  On the other hand, simply fixing the error as I type my reply is a non-issue for me (effort-wise).