I was surprised that this fixed a stuck trackball in ten seconds after an hour of messing with it.

Fold a paper towel several times and soak a small area in rubbing alcohol.
Hold the blackberry facing downward with this moist area of the towel between your finger and the trackball.
Rub the trackball in a circular motion until you feel the trackball running in all directions smoothly.

With the Blackberry facing down, only a film of alcohol is carried to the "gunky" rollers by the trackball.

Good Luck!