I found that with Ubuntu 9.04 x86-64 disabling compiz/beryl(desktop effects in GNOME -- not sure if xfce wm supports that as I haven't run an xfce is some time(was testing it as a more featured replacement for fluxbox on an old nb)) solved the freezing on wake from sleep/hibernate for me...
It'd be really nice if 9.10 final actually fixes that, along with video playback also occassionally freezing the machine after wake from sleep. (It doesn't happen all of the time now, so they must've at least made a partial fix for it so far...)
(4850 mobility 512MB GDDR3, P8600)
Sager NP8250-S Core i7-4800MQ/780m/32GB/128GB SSD/750GB Scorpio Black/1TB WD Blue(7mm) (win7 x64 pro)
Acer Chromebook C720(i3-4005U/4GB) 128GB SSD(stable/crouton xfce)
DIY ASUS P9X79/i7-3930k/64GB/multiple multiple terabyte HDDs(mostly WD 10k)/780 Ti SC (win7 x64 pro/Ubuntu 14.10)
DIY ASROCK 990FX Extreme9/FX-9590/32GB/multiple multi-TB hdds/R9 280X