I hesitate to summarize Boundin' with the massive cliché that is Just Be Yourself, so I'll try to throw a little spin on it and say that it is more about being confident in who you are rather than your appearance. Clearly, since the short film starts with the story of a sheep that is so happy and content that it constantly bounces around singing, and thus doesn't give the impression of being insecure until suddenly it is Unceremoniously Plucked From Its World and sheared naked of its wool, it is more about self-confidence than just being yourself. On the other hand, maybe that's just two ways of saying the same thing.
At any rate, the movie received something of a lukewarm reception from viewers, who either loved it or hated it or wanted to love it but thought that the sheep wasn't cute enough or something. I appreciated the fact that Pixar was able to tell the story using such simple means. The entire film takes place on the same 10 square feet or so of setting, and there are only two characters (unless you count the little animals that laugh at or cheer the sheep, depending on his level of security).
I also liked that the movie did something original with the dialogue. Many of Pixar's charming short films are silent, and I really thought the singing worked great because it had such a good Dr. Seuss-like ring to it. The moral is simple, but the emotions created are real. We pretty much know where the plot is going, but we still sympathize with the sheep after it is originally shorn, because in truth it really does look ridiculous.
Where Pixar should be especially commended, however, is that later in the film the sheep is shorn again, plopped back down on its rock, but no longer looks ridiculous, simply because of the sheep's casual behavior. He doesn't look ridiculous because he no longer cares so much how he looks.
And if you think the sheep or the jackalope were just not cute enough, maybe you should write a whiny little song about it