Why do I have to reboot my iMac and Wacom Cintiq after sleep? I have an iMac and a 24 inch Wacom Cintiq. When I put the iMac to sleep, it freezes and I have to restart both the iMac and the Wacom Cintiq. 

How can I get around this?
I've had the same issue with my MacBook Pro (Early 2009).

Only occurred when waking up from sleep initiated by lid close. 

Workaround I used was to switch off Automatically adjust brightness (Systems Preferences -> Displays). Hasn't re-occurred since – try that and see how you go.