Low-rep users are getting around the 50 point minimum by posting their comments as answers. Comment-answers are pretty common (example from a few minutes ago), so is there any way to deal with them before the user presses the Post Your Answer button?
Almost all of the comment-answers are short and contain a sentence or two. I'm not sure what percentage of the low-rep users write decent 30 character answers, so maybe a nice message should remind them that their comments shouldn't be posted as answers:
I'm guessing that these new users are getting frustrated that they can't post comments. Maybe displaying a dummy add comment link that brings up a popup that says that they're X rep short of comment privileges would let them know that they cannot make comments yet?