Lets do everyone a favor and keep this discussion clear of the negative talk. We all know the risks involved, but for whatever reason, we want to use a raw disk.
I also have need of this solution. I was using raw disk access on a Windows host, but have changed the host to Linux. I am not having difficulty. I believe I have gotten one step further than the others on this discussion in that I was able to assign the disk to the guest and boot up.
You have to make sure the user running VirtualBox has read/write access to the device. The way I accomplished this was assigning the disk group to the user using the adduser command.
So, like I said, the guest booted fine, then when I tried the access the drive on the guest (a Windows guest) it froze up on me and I had to power down the VM.
I had not unmounted the device from the host file system, would that have caused a problem? Any thoughts?