I wonder whether it's good form to edit blog posts after they are published. It seems fine—I'm not changing the message of the post; just correcting typos, adding additional links to relevant content, and sometimes updating the unclear parts. I've done some looking and the most recent posts I've found from others (so far) are from 2010.
There's the Search Engine People Blog's article, 10 Reasons For Editing Your Published Blog Posts, which makes a few good arguments in favor of editing posts. The article's good ideas are common sense, like correcting typos and optimizing SEO. One of the reasons they suggest you edit posts is that "you can and it is easier than writing new blog posts" though, and I totally disagree with that. "Just because you can" smacks of laziness.
Then there's Is it okay to go back and edit your published blog posts?. It covers much of the same ground: typos, errors, clarification, and updates. Linda also suggests if you want to change things that it is a good idea to make notes where you've made changes. (e.g. [I edited this part on April 20, 2012].)
Additional thoughts on editing posts
Proof-read first, then publish. It's better to take a little longer in going live than to hit the publish button on an error-laden article. If you're racing for a scoop, so be it, but be ready to go back to correct errors as soon as possible. An article loses a chunk of credibility when it looks like it was written by someone that can't use spellcheck.
Don't change the thrust of an article. This should be a no-brainer. If you said it, you said it. Given the internet's knack for remembering past errors—and taking screen grabs of them—you aren't likely to have much luck deleting your past. This is especially true if you said something really awful.
It's good to update posts that are out of date with new information when available, but don't neglect the homepage. The best route is to write a new article, then edit the old ones with a link to the updated content. That way, the homepage gets a new article with fresh content, and the old indexed pages can still reference the newest information.
I dislike feeds that only show snippets. But if your RSS feed uses full articles, editing an article that is still in the feed can cause the post to show up in your subscribers' feeds again. I'm sure there are ways around this, but I haven't found them yet, with the exception of getting everything right the first time around.
Maybe I'm overthinking it
It all comes down to being ethical, moral, and judicious. Edit well. Edit smart. Don't try to cover things up. And if possible, try not to annoy your subscribers in the process. It's common sense, but then, common sense isn't so common. What do you think?
Updated May 10, 2012
Just found this article from BlogWorld, asking Is it Ethical to Edit Your Blog Posts? The conclusions are similar to mine. It's fine for clarification, updating opinions, and correcting errors. It's not okay to make sneaky changes or try to hide the fact that you said something.
Updated June 14, 2012
Oliver Reichenstein, of Information Architects, just published an article on how to handle some similar issues on Twitter. It's well thought out. Some have claimed it would add complexity, but the implementation Reichenstein suggests is quite simple and elegant. (Typical of IA.) It would be nice to see Twitter implement something like this.