One of the most annoying things about Facebook is when you post a comment with a typo and then you can't even edit it. Facebook has at last rolled out the ability to edit comments, catching up with Google+ which has had the feature since launch.
The feature is rolling out to everyone in the next few days. It'll only be available on the web though but with phones these days all having auto correct features it shouldn't be too much a problem for mobile users.
Now you may be thinking you had the ability to edit comments anyway. But what Facebook did was give you a short time limit after posting a comment to edit it again. So you couldn't come back tomorrow and edit the comment. Now you will be able to edit the comment whenever.
A few drawbacks are that people can see the edit history. So you still have to be careful about what you post. Also you can't go back and edit previous comments.
It looks like Facebook also won't be allowing people to edit original posts. I can see why this is because if someone where to post something really controversial and it gained a lot of comments, they could easily change it, making the whole discussion make no sense.