[conspire] ro, noatime, ...

[Michael Paoli]

And, where feasible, even more efficient than noatime, is ro.  E.g. most
of the time, I have /boot and /usr mounted ro.  I also specify the
noatime option on those filesystems (why bother to have them mounted
atime when mounted rw, if they spend most of their time mounted ro
anyway).

Also, for apt dpkg based system (e.g. Debian, likely also Ubuntu and
others), a bit of suitable apt configuration, and those filesystems will
automagically be remounted rw when one updates software/kernels, and ro
again when done (at least much of the time - the remount ro will fail in
some cases - e.g. unlinked file is still open (such as outdated removed
library is still in use by some PID/application that stated before it
was removed) - in which case apt complains that it wasn't able to
remount it ro, and it simply remains mounted rw until otherwise
(re)mounted ro - e.g. such as upon reboot).  Anyway, example
configuration bits:
$ head -5 /etc/apt/apt.conf
DPkg
{
    Pre-Invoke {"mount -o remount,rw /boot"; "mount -o remount,rw /usr"; };
    Post-Invoke {"mount -o remount,ro /boot"; "mount -o remount,ro /usr; :"; };
}
$
I think some Debian, and/or Debian based distributions may automagically
configure such automatic remounting of /usr filesystem - at least if
/usr is separate filesystem, and perhaps if it's also normally
(/etc/fstab) mounted ro.  I haven't yet, however, seen that
automagically done for /boot.
One can of course also manually remount rw when needed.  E.g.:
# mount -o remount,rw /boot && { vi /boot/grub/menu.lst; mount -o  
remount,ro /boot; }

references:
http://linuxmafia.com/pipermail/conspire/2010-March/005420.html, et. seq.