Here is an interesting article at the CNN website about Anderson Silva's front kick to Vitor Belfort's jaw:
In my style, kicks are generally no higher than the waist and are usually aimed at the groin or knee areas.
My Kenpo friends like to say, "If you want to kick to the head, take the attacker down first (then stomp him)." Not that I would necessarily do that... just that I have heard that. Of course, I would do everything possible to avoid an attack.
Charles C. Goodin