Andrew got me a yarn ball winder for Christmas (I asked for it) and had a lot of fun winding my old balls of yarn into new balls of yarn. It sounds like such a silly thing to get excited about, but I was really excited. :) You may ask why do you need an apparatus to wind your yarn when you were perfectly capable of winding balls of yarn on your own. The answer to that question is tension. You get a more even tension with the winder than with your own two hands. I've actually had some yarn that was wound too tight and when I went to use it on a new project there was a distinct difference between the old and new yarn. The yarn ball winder is the solution to that problem.
These are my yarn balls before.

This is the yarn ball winder finishing up a ball of yarn.

These are my yarn balls after.

It's silly but the new yarn balls make me happy. :) Just look how nice they are and they're not going to roll away and the tension when you use them is so much more even than using a regular yarn ball.