I'm guilty of doing stuff like this.. When I write a node, even though I may preview it and it may look fine, I always go back and re-read through some of my posts (esp. if they're garnering lots of rep), and frequently change some wording slightly, clean up code occasionally, and sometimes add to it.
in reply to Knowing when nodes are updated
Though when I am making a significant content update, I will make it obvious with an "Update:" stamp. Unless I make the update within a few seconds after I post it (which, alas, I also do frequently).
I do try to take heed to replies, though, beforehand, so I don't change things that invalidate someone's reply and make them look stupid. That's just rude.