I'll add one other thing about foot strike and training strategy. I strongly believe that cadence (number of steps per minute) is one of the most important aspects of running efficiently, and more important than whether you are a heel/mid/fore striker. The higher the cadence the more likely you are to have an efficient running style. While everyone is different, ideally your cadence should be above 180 steps per minute when you are running at race pace. When I first got my Garmin 620 one of the first things I noticed was that my cadence was in the high 160s and my stride length around 1 meter. I made a concerted effort to try and move my feet quicker (it took months for it to become natural, so make the progression slowly). Upon research, I found that the less your foot moves forward and kicks backwards the less energy is spent bringing it back into position for the next strike. This means when I run it looks more like a quick shuffle then an actual run with legs kicking way back (its why I don't do well on non-road surfaces because I barely pick my feet off the ground). I believe the reason you see elite runners kicking their feet way back is because they're running a 4:00-5:00 min/mile so unless you're going that fast a quick shuffle might be better. I now consistently see my cadence in the high 180s to 200 steps per minute and yet my stride length has naturally elongated to 1.2-1.3 meters. Keeping my feet to close to underneath my body has also reduced my injury rate.
One thing I always like to tell myself when I'm running is to "Run Like a Ninja". When you see ninjas run, they move their feet quickly and quietly. If you emulate that, you will reduce your chance of injury and it will likely enable you to run further faster because you will use less energy per step.
