Here is a handy little trick with awk to print out the FS's that are over 90% full:

	df -k | egrep -v "proc|fd|cdrom|mnttab|run|tmp|Filesystem" | sed 's/\%//' | awk '$5 >= 90 {print $5 "%\t" $6}'


You may need to change $5 and $6 for your version of df.