Does running through the rain help keep you dryer? This interesting piece written by an astrophysics expert and fellow with the Royal Astronomical Society breaks down your chances of getting wet mathematically.
Because the human body is a complex thing -- with different shapes and body parts moving in opposing directions -- the actual equations are far too difficult to calculate. However, by cheating a little bit in the form of averages and assumptions, it's possible to come up with a useful approximation.
The solution that gives you the minimum chance of getting wet (other than not being in the rain at all)? Exactly what most people do instinctively -- identify the nearest shelter, and then run to it as quickly as you can.
Interestingly enough, if there isn't shelter nearby and you have to stay out in the rain until it stops, running will actually make you wetter, because you will be moving your front surface through a "rain field," scooping up water as you go.
