How many times do you see a very short comment and think "I guess they didn't know there was a minimum length to get your 25 points for the comment!" We love meaningful comments! "This is an excellent post! Thank you for sharing this post." may in fact be entirely sincere by some, but it also typifies a copy/paster "I'm doing this comment JUST for the points!" type person (for more info, see Miss Manners Guide to Commenting Philosophies)
Well, let's not start counting our characters in our comments, but it does take a minimum of 50 characters in a comment to get our 25 points. (I previously relayed something that I had heard, namely that it takes 10 words or more, and while that is approximately right, it is more precisely a character count, I just now tested to confirm it!). So when you comment, you should fill up at least half a line of the commenting box (compare my red arrows in the diagram below, the 50 character point is just over half distance of comment area width).
Points are nice to get and we might as well earn them for making a comment, so make sure you are aware of this when commenting. Don't just say it was nice... tell us why and what part in particular! (and you will have no problems with points, AND you'll be making many more points in the eyes of the author!)