Same problem here. I never sleep my PC, but I do allow the monitors and HDD to turn off. I tried disabling Hybrid Sleep in Power Management, hopefully that helps.
EDIT: I have a similar problem with my Precision M4600, but the XPS 8500 issue seems worse because even the mouse shuts off. Judging from my experience with that machine, it seems setting the monitor to automatically turn off (whether via sleep or idling) causes the issue. Gonna try changing those settings and seeing what happens.
