Hi all, just had the following given to me by the BlackBerry team:
Grease and dirt can collect underneath the trackball which can make it less responsive. Pressing down hard with your thumb and rotating the trackball can help to clear the dirt and maintain your phone. Repeat in several directions until responsiveness is returned. It’s a good idea to remove the battery first to avoid accidentally pressing any buttons whilst cleaning.
Hope this helps those who may have been experiencing problems.
Cheers,
James