I'm trying to enter a comment on SO, and when I hit Add Comment it just prints "4 more to go.." in grey underneath the comment box. Does this mean I don't have enough reputation to enter a comment? I did yesterday. Plus, it's my own question!
As others have said, there is a minimum 15 character length for comments.
Also, you don't yet have enough reputation on SO to comment on all posts. However, quoting from the FAQ, "you can always comment on your questions and answers, and any answers to questions you've asked, even with 1 rep."