This is a very efficient and effective way to do it.. all you need is inotifywait (in inotify-tools package, and of course inotify enabled kernel which is pretty standard these days).
while inotifywait -qq -e modify $LOGFILE; do
x=`tail -n1 $LOGFILE | grep "something"`
if [ "$x" != "" ]; then
echo $x | mailx -s "Something happened!" firstname.lastname@example.org