I just figured out a solution to my problem, but I thought the more web pages providing the solution on the 'net the better.

The problem:  When I brush a stroke in photoshop with the pressure set to brush size, sometimes it works and sometimes it doesn't.   It is very irritating.  Sometimes I get a nice pressured line and sometimes it is just a fat plain old mouse click line.

The solution:  
Go to your Wacom Tablet Properties panel, double click on your tablet icon and change the current mode from 'standard mode' to 'recognition data'
Thanks conceptart.org

and a few more threads from them if that doesn't fix it for you
http://www.conceptart.org/forums/showthread.php?t=199564
http://www.conceptart.org/forums/showthread.php?t=202736
http://www.conceptart.org/forums/showthread.php?t=201668

I've only recently installed my Intuos3 on a new computer so I haven't had a chance to play with the settings but I had a look anyway and it was already set to 'recognition'. Maybe that is the default and you changed it?

i don't think so.  I had the problems so i uninstalled all the drivers then re-installed them again and didn't change that setting.  I didn't even know there was a setting there to change!