Updating Blog Posts
I often post something, and then a little while later, add some updated information. Other bloggers do this as well, it's a common occurrence. But I've noticed that with Google Reader, some readers never see these updates.
Google pulls the RSS feed as a result of a ping being sent when the post is created, but then when the article is updated, they apparently don't fetch the updated content (or at least not right away), so Google Reader users will continue to see the old content.
If you posted an article and it got a bit of attention, there will be links pointing to it. In this case, you really don't want to delete that item and post a new one, because those links will go 404. Depending on the extent of the change you're making to the original post, you could either add text to the original post and post a new item with a short message saying "There's an update on this available here" with a link back to the original post, or you could post the update information in a new post and update the original with a link to the new post.
I think the latter is probably preferable, so users reading offline have the new content available to them, although it would tend to fragment comments. Some commenters would comment on the original article, but since the "thread" of the original article now ends at a different post, others would comment there. If this is an issue, make the newer post nothing more than a link back to the original to encourage users to comment there.
But you always need to post a new article to flag that the original was updated, even if you only posted it a few minutes ago, or some users are going to miss out on the updates.
(If you find yourself doing this a lot, consider using your blogging system's ability to schedule posts - have your post go out in 3 hours time, so you have those 3 hours to edit before it goes live).