host OS Windows 7 64 bit SP1, RAM 8GB, CPU Intel i3 2120
VM created using 8400.0.amd64fre.winmain_win8rc.120518-1423_server_serverdatacenter_en-us.vhd, 4GB RAM, VT-X and nested paging are enabled, the USB controller is disabled, audio is set to null, PAE is enabled, 2 virtual CPU cores, network is set to bridged
After a few minutes from VM startup, the guest OS logo animation is running, the VirtualBox hdd activity icon is stuck on red, the host's hdd is doing something intensive (the case hdd led is always on). Clicking on the top-right X window button to bring up the Close Virtual Machine window, VirtualBox hangs. After forced termination of Virtualbox and VboxSVC, VirtualBox reports that it can't access the vhd image. Overwriting the vhd file fixes this.
The first time I tried it, I waited over an hour for the guest OS to complete its preparation stage, but it didn't and I lost patience.