When your computer mouse quits rolling smoothly or starts to cause the cursor to 'jump' around the screen, you don't need to replace it, its just time to clean it out! I have to do this about once a month.
Start by removing the bezel that holds the ball in. This can be done by pressing two fingers on the piece and turning counter-clockwise. take the bezel off and remove the ball. You will now see three places where the ball touches points inside the mouse. You will recognize them by the black, fuzzy ring of dust that is wrapped around them. This fuzz is what is causing the problems with your mouse and it's what you want to remove.
Removing the fuzz can be done with tweezers, but I prefer to use my fingernail. It is best if you can scrape the fuzz ring off gently so the strip of fuzz remains intact. When it is all scraped off, you can remove it in one strip. It's okay if the strip breaks or if you have to remove it piece-by-piece. Just make sure you blow into the mouse (or use canned air for electronics cleaning) before replacing the ball and bezel.
That's it! Your mouse should now roll with ease!