Like publius, I permit myself only a fairly short amount of time to change the substance of something I post. I may update or make a follow-up post, but after a relatively short window of time, when I’ve posted something I just leave it there.
But unlike publius, I do not limit myself in time to correct purely grammatical issues. If I find a spelling or grammar mistake in my own work — and these are frequent, I admit — I’ll go back and fix it later without any kind of notation. In theory, I will do this for posts going back to the very start of the blog more than four years ago.
The difference in my mind is that between form and substance, and substance is more important than form. If form gets in the way of substance, it should be changed. If substance changes, though, it seems intuitive to me that I ought to acknowledge that.
As for comments, my thoughts on comments are on record in the FAQ, posted to the right.
Regarding your poll, I don't want to see much of a change. I liked all the selections except for chick photos(assumed that was a joke) and the food recipes. I don't have a problem with them, just don't read them all word-for-word.