I work only SP games, and there are times when I've been hit with a foul ball or a ball that bounces up off the plate or ground. Usually, it hits my legs, and that's no big deal. Lately, I have been worried about taking one in the eye (probably because I recently DID take one in the eye), so I've been wearing some Coyote sunglasses (got 'em from Amazon.com for $20) that come with different lenses: dark, orange and clear. The orange helps with overcast games (any shooters out there will give the thumbs up to that one), and the clear lenses are good for night games. It's just one less thing for me to worry about.
Taking one off the collarbone is no big deal. I've had it happen once, and it didn't do anything. Forehead? No big deal. Nose? Mouth? Doesn't take much to break a nose or split a lip, so my advice is to only worry about that area and don't worry about all the rest (so long as you're wearing a cup, but if you do FP games, you probably already know that one).
Mike must have some Jedi or Matrix thing going on, because even though my reflexes are pretty darn good, I still get hit. Resign yourself to that fact, keep your head focused on where it's supposed to be (nice and still - don't dance), and you'll be fine. That cut on your lip should heal in 3-5 days.
Though this does raise a good point: why DON'T we wear masks in SP? It's so easy to break a nose and have a pint of blood pour onto the field, and losing an umpire to a broken nose is just... well... silly.