I don't know the distro you're using at the moment (maybe Ubuntu?), but for Slackware there's a straight way to detect a graceful shutdown.
If you add this line:
to the /etc/rc.d/rc.local_shutdown script, every time you shutdown your computer right that file is created and, on next reboot, Slackware boot scripts search for it and, if found, fsck checks are skipped and that file is removed.
I guess you can adopt this approach on every distribution, given you tailor it to your boot process mechanics.