> So here's the final analysis, if you want to stay as dry as possible: If the rain's coming at you, go as fast as you can. If the rain's at your back, go at exactly the same horizontal speed (i.e. move so that the rain appears to be falling straight down).

Like Don, I'm confused about what happens at the border case of rain falling straight down. It doesn't make logical sense to me that if the rain is falling at you at 90.00000001 degrees, that you should run infinitely fast, while if the rain is falling behind you at 89.99999999 degrees, you should only walk at what would be a snail's pace, because there would be VERY little horizontal rain speed.