This is info from Doug Barton; I'm sharing because it's interesting (and relevant):
This is an FYI to let people know about a really nice feature for those
that have ports installed which include kernel modules. You can place a
list in /etc/src.conf like this:
PORTS_MODULES= emulators/virtualbox-ose-kmod sysutils/fusefs-kmod x11/nvidia-driver
which will cause those modules to be built and installed with all the
proper matching stuff at the same time as buildkernel and installkernel.
This feature has existed for a while, but has had "issues." Thanks to a
team effort it's a lot more robust now, and ready for prime time (in
HEAD, and the -STABLE branches for now, soon to be in 9.1-RELEASE).