Jumpy Mouse Pointer
Problem: Mouse pointer sticking. Pointer will go up and down and to the right ok, but has trouble moving to the left.
Hardware: Balled Mouse
Resolution Steps: My first thoughts were dirty rollers. I popped the ball out and there was indeed a little bit of fluff around the rollers. I removed this and tested the mouse; still no leftward movement. Conclusion: dirty rollers wasn't the problem.
Sometimes the wires in the mouse's tail can break, so I moved the mouse's tail around a bit to see if it made any difference; unfortunately it didn't. Conclusion: the mouse's tail wasn't the problem.
The next thing to check were the mouse drivers. I plugged in another mouse and it worked fine. Conclusion: the drivers or PS/2 mouse port were not the problem.
Time to crack open the mouse. This mouse has a single screw hidden underneath one of its plastic sliders (the rear slider). The sliders are glued into place but with some careful manipulations with a small flat-headed screwdriver it's possible to remove them without destroying them. Removing the screw allowed the mouse casing to be opened up (there's a hinge arrangement at the front of the mouse, so lift the back up and then the top-half of the mouse will pop off). Careful inspection of the rollers showed that the one that detected horizontal movement wasn't clipped in properly; the end pin had popped out of its holder.
I clipped the roller back into place and reassembled the mouse. Upon plugging the mouse back into the PC it worked flawlessly.
Conclusion: don't throw out that mouse just because it's not working 100%!