Interesting and frustrating problem, well 2 problems...
I seem to have somehow caused the '/' partition to become read-only
AND my /etc/vfstab entry for '/' has this error:
the mount point is /dev/dsk/c1t0d0s0, and
mirror /dev/md/rdsk/d0 is set as the 'filesystem to fsck'.
After much hunting, searching, and thinking, I believe I've found a solution:
Did I mention that my root (/) partition is mirrored?
This is how my mirror...