According to the Wacom Community forum, the Intuos 3 seems to have this common problem.
This was the solution posted by user LuuKen:
here is what you have to do..
win7: go to. Control panel -> System and Security -> Administrative Tools -> Services
Vista: go to. Control panel -> Administrative Tools -> Services
okey scroll down the list and find "Tablet PC Input Service" right click it go to properties and disable it. this disables all the tablet functions in windows.. wich are overriding the wacom drivers if it's left on.
i believe this is an issue with the new driver 6.1.6-7
i rerolled to the older one 6.1.6-5 before i did the above.. it worked for me. alot of people have this issue..
in anycase everyone should dissable it. it will make your brushes run more smooth
You may also see if there is a driver update for your tablet.