I'm using a Wacom Intuos2 graphics tablet in OS X Snow Leopard 10.6.2, which works great, 80% of the time.
Every 20 minutes or so, OS X to just start ignoring input from the pen. More specifically, only the pen tip is ignored - the side buttons on the pen still work. Putting the Mac to sleep and waking it back up restores functionality to the pen tip.
This is using both of the latest Wacom drivers claiming compatibility with Snow Leopard: versions 6.1.2-5 (Nov 25, 2009) and 6.1.3-3 (Jan 21, 2010). I have no experience with this tablet with other version of OS X / drivers.
The tablet works 100% in Windows, which leads to blame either OS X or the OS X drivers.