I have had my system freeze several times now when doing multiple files copies in DO when using Win8 Consumer Preview. Usually, I am copying over a LAN. The whole computer will freeze (the mouse pointer will be able to move around but clicking does not work). I have to do a reset to get it back up and running. I am not using the new queued file copy of DO but the old method of having several copies going at once in their own window. It was NOT an issue at all with the DP version of Win8.
I expect that unless it is a Win8 problem, you will hear more about it over the next few months...
User-mode applications like Opus cannot generally cause the whole computer to freeze by themselves. Opus may be triggering a bug in your system, but the bug is elsewhere; most likely in the motherboard or IDE/SATA/network drivers (or possibly the gfx drivers, due to all the activity in the progress dialogs) on your system (which quite possibly need updating for Windows 8).
Yeah, I have found that there is a program called HWmonitor that will cause a lockup every single time (along with AIDA- new Everest) so something is going on with hardware interrupts. Well, Win8 didn't cost anything so I guess I get what I paid for...