Deprecated: FreeBSD as a PV DomU
FreeBSD has gotten Xen support in fits and starts over the last few years. An internet search will show a port of FreeBSD 5 to Xen2, http://txrx.org/xen/ freeBSD 7 to Xen 3.0.2 http://www.fsmware.com/xenofreebsd/ and some chatter about support in 8-CURRENT.
update: it is in 8-current http://wiki.freebsd.org/FreeBSD/Xen and now has a mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-xen
Now, to the best of my knowledge, most of the work for all of these was done by Kip Macy. (thanks!) I just want to make it clear, all I'm doing here is documenting the install and (maybe) making some tarballs of the results of my compilation available.