Well, so far I've only edited each of my posts five or six times. I need to set up a policy for corrections. Generally speaking, grammatical errors will be corrected as soon as I notice, with little or no notification. Substantive and/or factual errors will be corrected in updates to the original post.
Update: Like so. This applies to any correction made more than a few minutes after the original posting. If I notice a mistake right after it goes up, I may just fix the mistake without indicating it--but only if this happens right away. Updates to the original post will only be made on the same day as that post. After that, corrections will get a new post.