Well, here is my first try:
#!/bin/ksh
set $(df -v |grep -v ":" | grep -v "Mounted on" | sort -k 5 |tail -1)
echo "DISK" $9 is $5 "full"
exit
The above doesn't take NFS mounted filesystems into account,
but this can easily be changed (remove the ' grep -v ":" ' part)
wmp