Disclaimer, I didn't actually make this pin, but a friend of mine did on a craft night I recently hosted, so I'm including it.
Pin: DIY: Mosaic Ornaments
Pin rating: TERRIBLE
It is very difficult to cut the cd's, and the chance of cutting one's self accidentally is high. The end result pictured on the website, even for talented artists, is difficult to achieve, and the reward (even when it does look great) is not worth the time or risk of injury.
It may work better if you have heavy-duty scissors and can cut very small pieces, but overall I would NOT recommend this pin. :(