Recently my system has been panicing about once a day, always during
heavy disk activity, with the message "free vnode isn't". It's so bad
that not only can I not make it through an entire "make build", but
/etc/weekly kills it, and even running a build of a much smaller
project on another machine that uses the NetBSD box's disk makes it
die.

I'm about to try turning off SOFTDEPS in my kernel config, just out of
superstition, but thought I'd see if there's a known problem. My
sources are up-to-date as of about January 5, I think.