wlennon,
bs aside, your optimum crank length is a compromise between pragmatic issues and your femur length. Think about how your leg works. Your whole leg length more or less sets how high your saddle goes, but your calf is just along for the ride. The actual difference in height from top of stroke to bottom is determined almost entirely by your femurs. As your femur lengthens, your knee will describe a bigger circle with each pedal revolution. You'd like to have your pedals roughly follow suit -- so if your femur is longer, generally you'd go for a longer crankarm.
That's just for starters. Then look at how you ankle. A good and supple track rider will point his/her toe down at the bottom of the pedal stroke and then pull upwards on the back stroke, with the toe still pointing down. Watch Chris Hoy start a kilo or most top sprinters on the backstroke and their toes will be pointed almost straight down while they're pulling up on the pedal. This has the effect of increasing your leg length overall, but it also takes up part of your pedaling circle.
Then come pragmatic issues: Longer crankarms need more leg velocity to achieve the same pedal RPM, which makes them more sluggish when you need a snappy acceleration or when your legs are tired. But longer crankarms give you a bit more leverage if you have to push a big gear. Then there's the matter of what you might ride on other bikes -- most riders' knees don't handle changing crank arm lengths all the time. Plus, consider your pedal height, how far forward or back on the pedals your feet are located, and simple issues like pedal clearance on a steep track or tricky roads. If you have to ride around a lot of curbs, you may just want a high bottom bracket and short cranks. Getting track cranks in 165 mm is pretty much a safe bet -- you don't hurt your knees easily with cranks that are too short, but the same isn't true if they are too long, and you can always sell 165's easier than any other size. Sugino's come in 2.5 mm increments from 162.5 to 175 (Shimano's go from 165 to 180), but at a track you'll find 165, 167.5 and 170 cranks almost exclusively. Definitely don't worry about the long cranks you find on the road or mountain.