If you're a savvy Facebook user, you probably already knew that Facebook had a ninja-edit setting that allowed you to edit your comment by clicking 'x' right after you posted. This would bring up the comment text and allow you to make changes and repost without duplicating your comment or deleting and starting over. This feature was handy, but it had its flaws. The option was only available for a few seconds after you hit post, and the comment became permanent if someone posted immediately after you.
Now Facebook is rolling out a fleshed out version of this feature. Now, when posting comments, you will see a little pencil symbol in the right-hand corner. Clicking this will bring up options to delete or edit your comment. If you choose to edit, your comment will be updated to include 'edited' hyperlink. Anyone who clicks on this will be able to see all versions of the comment, including the original, unedited comment.
It's a nifty feature, and one that many will no doubt find useful. The fact that it preserves your error forever in the edit history is less nifty but necessary if we're to prevent people completely altering statements unbeknownst to their fellow Facebookers. Oh, and in case you were wondering, this new feature is available for new and old comments. Edit away!