Following on from the excellent turbotortoise post on cadence, I chipped in with my opinion that if you are naturally quite a low steps per minute runner, that upping the cadence and taking smaller steps has a significant impact/improvement on times.
I'm not a super-runner - I am 42, about 15 stone, and my best time before I started looking into this more was 33 minutes and 5 seconds for the 5k.
In the last couple of weeks, when I've switched to a very conscious attempt to increase the cadence, I've found an improvement to 31:35.
What I also found was that (1) it changed my breathing pattern quite a bit - from every 3 steps to every 2 steps; and (2) that it has been much kinder to my knees. I don't have a medical problem with them, but pounding on them before did bring about some pain in the post-run glow (and through the evening).
Today, even though I went 10k last night (where using a faster cadence and smaller step also improved my time by 5 minutes to 1 hour and 7 minutes, with a negative split of 34 minutes to 33 minutes), again no pain at all from mr and mrs knee.
Thought those of you with troublesome knees may find this interesting