Stretching allows more flexibility in your muscles. period. The more often you stretch, the more toned your muscles will be, and they will, in general, respond more favorably in all physical activity. If you stretch lightly before you run, realizing your muscles are cold, then it can be beneficial. The key is to listen to your body. What works for one doesn't necessarily work for another. Personally, I don't stretch my cold muscles, but this comes from years and years of listening to my body and perfecting my routine.

And this is the key for the way you run as well. Pay attention to how you are striking the ground. Trust me, you will be able to tell if you heel-strike or not. If this is still a little ambiguous, pay attention to your legs. Heel-strikers tend to have more problems with their knees because they naturally hyper-extend the joint if they are running hard (in order to actually allow the heel to strike first). In the beginning literally talk to yourself in your head, "ball first, ball first" (meaning ball of your foot) or "toes first, toes first", and it will feel really awkward to strike anywhere but the heel first, but it will help.

You don't (necessarily) need a running coach. You just need to be aware of what works for your body. Run consciously until you run (correctly) from habit. You will know it is correct (for you) based on how your body responds.

..it doesn't reduce the impact but it gets the muscles ready. Here is a nice little article which explains a little something, something about stretching.
http://www.coolrunning.com/engine/2/2_1/126.shtml

Nothing like getting personal on EF is there buddy? I quite like my 80Kg hulk, it's just the green body that scares the gals away Next time, you can lead the snow shoe trail up Mt. Whateveritsnameinglaruswas....

This is what I agreed to!

What Niranjan is disagreeing about is it being open to debate.

I think here it all depends on the interpretation of stretch. Whilst sticking your shoes on and immediately sprinting up a hill as fast as you can will definitely lead to injury, immediately getting into a lunge position and stretching out your hamstrings as far as they go will also lead to disaster.

Consider a stick of chewing gum (yeah, bear with me here...). When you take it out the packet it's fairly rigid and with a sharp pull you can break it in half. However, warm it up sufficiently (chewing it being the traditional method) and you can twist it, stretch it and bend it into all manner of shapes and sizes without problem. Your muscles are exactly the same. You need to gradually warm up the muscles before you can really stretch them, hence the modern trend for stretching *after* a run, rather than before.

What you need to do *before* your run is warm the muscles up. Best way to do this is to simply walk or jog lightly before getting underway.