Any news on the USB 3.0 front?
edit: I think the reason is that suddenly one of my hdd turns off. I can hear that they go in sleep mode (the typical noise). After that the system freezes. Since my 10.8 is installed on a SSD I can't really tell if there is the same problem with the SSD. Any idea why this could happen (maybe unmounting the drives automatically).
I'm not sure if I'm having the same problem as you, but after the system working fine for a few weeks, I've now twice found the system unresponsive when I went to wake it after being away from it for a few hours. I don't let the machine do a full sleep or even turn the hard drive off, just the monitor after 20 minutes. I have to do a hard shut down (hold the power button down for 5 seconds) and restart to get it going again. Did you ever figure out your problem?