I used to have this phone and I notice the trackball had a lot of issues. I dont think this 'fix' was ever mentioned in this forum but when the trackball is not responding, part of the reason is that there is a lot of dusk stuck on the ball. One of the 'easiest' temporary fix without taking apart your phone is to do the following

1) Get a blank piece of paper and lie it down on a flat surface (like a desk)
2) Turn off your tour or set it on keypad lock (or else we might accidentally hit something) Password lock is not idea because you might hit the emergency call button by accident.
3) Flip the tour down (screen first on the paper). Gently applying some pressure (gently!) push down on the middle of the phone rubbing the trackball on the piece of paper (go up and down and/or left and right depending on which direction is giving you the issues)
4) You should have fixed the issue, repeat step 3 if necessary.

Most of the time this worked for me, hopefully this will help any other existing tour users out there. If not, its probably time to upgrade to a BlackBerry 7 phone! (Bold 9900 has a bigger keyboard and is awesome!)

Hope this helps!

PS this only works for the Tour 9630 all other devices use a different type of trackball than the tour.