usbd_enable="yes" in /etc/rc.conf can cause a server to be unable to reboot without manual intervention
I installed 3.8.2 from a CD on a server the day before yesterday, the default /etc/rc.conf that came with it, modified initially by me only for the networking setup, had usbd_enable="yes" in it. When I tried to reboot, after stopping sshd but before getting to devd, it just stopped. I came back in person the next morning and just hit ctrl-alt-delete, and it resumed the reboot process and booted up normally. I changed the usbd_enable="yes" to no, and that fixed the problem.
i don't know if this affects all hardware or just the supermicro I ran this on, but unless you have physical/ipmi access to a system, this would make reboots impossible remotely.
Does the box have /usr/sbin/usbd?
It should only exist on systems compiled with WANT_OLDUSB but not for usb4bsd which is the default. The /etc/rc.d/usbd script has a check so it will do its thing only if /usr/sbin/usbd exists and thus be a no-op on default usb4bsd systems.