There is a preliminary port of VirtualBox for FreeBSD (see the -emulation list for the port; it is not in the tree yet). There are a very few of us who are discussing it on the FreeBSD site, and I though I would move it here to talk about it with friends. So please let's talk!
I have installed W2K Server, complete with all 80-some patches, and it is working well and stably. I'd put its speed somewhere between the very old VMware (faster) and the qemu family. It does work on a multiple-core CPU, in contrast to VMware.
No tools seem to be available, so screen resolutions are very low (800x600); the Ethernet port seems to be OK.
No benchmarking yet.