This can be considered as an ethical question.
I was wondering if, when seeing someone's comment answering the question on which it was posted, I can add an answer based on that comment. Of course, that only applies if the commenter did not answer himself already.
When wandering across the site, I came upon a few comments that could be answers or that actually solved the problem (comment of the OP saying that "it worked") but which never turned to be posted as answers. This for various reasons, I would guess the main ones are : user got deleted / removed his account, user forgot about comment and question, user resigned from answering (for unknown reasons).
I was also wondering if the answer should be made a community wiki since the commenter deserves credit but all the credit that could be given will go to the answerer (which only maybe formulated the answer better).
If this was to be done, credit to the commenter and link to comment would of course be given.