I'm generally in favor of pointing out when a key edit (i.e. correction) has been made to an answer for the following reasons:
- It helps indicate to people who have already looked at your answer that they should give it another read.
- If an aspect of your answer has been mentioned in another answer or a comment, it's probably best to point out the edit so that the other comments don't look strange.
If it's just a matter of fixing typos, I don't think any indicator is needed.
If the edit makes the answer completely different, like adding a whole different possible solution, adding another answer may be in order since this gives people a chance to vote on the solutions independently.
Regarding the format for indicating an edit, " EDIT: " usually works well, or a lead-in explanation like " Based on the comments, this answer has been updated... " if you're feeling wordy.