> When you emerged grub-0.97-r5, this was displayed on your console:
> WARN: postinst
> *** IMPORTANT NOTE: you must run grub and install
> the new version's stage1 to your MBR.  Until you do,
> stage1 and stage2 will still be the old version, but
> later stages will be the new version, which could
> cause problems such as an unbootable system.

Yes, the ebuild writes that to the screen.

But silently, in the background (because every output is piped to 
/dev/null - how evil!), the ebuild calls grub with some commands inside 
your grub.conf.

If there's a setup-command in your grub.conf, it is indeed executed. So 
if that command is outdated (something you won't notice, since that 
command is not used by grub in any situation i know), the ebuild will 
execute that setup-command and write to some device's boot sector. How 
evil, again!

Regards,
   Sven

P.S.: here's the code from grub-0.97-r5.ebuild:

         if [[ -e ${dir}/grub.conf ]] ; then
                 egrep \
                         -v 
'^[[:space:]]*(#|$|default|fallback|initrd|password|splashimage|timeout|title)' 
\
                         "${dir}"/grub.conf | \
                 /sbin/grub --batch \
                         --device-map="${dir}"/device.map \
                         > /dev/null
         fi