They work.
You'll need to to build some of the ports.
You will also need to build the mesa and other dependency libraries in ports. Go to the howto sections at
http://forums.freebsd.org there are a few tutorials there.
Got the box running up recently. I use mine by doing nvidia-settings after I login.
Backup your original xorg.conf file with a name such as xorg.conf.orig.bak in the event you have trouble.