Tips: Length Does Matter
Getting a good fit on a bicycle is a big deal. Traditionally, we concern ourselves with all manner of dimensions: saddle height, saddle tilt, fore-aft position, stem length and rise, and handlebar width are just the tip of the iceberg, and if you want to size yourself up, Wrench Science offers a good starting point--just make sure you take all those significant figures with a grain of salt.
Crank length, however, seldom comes up in these discussions, and certainly applies to far broader swaths of riders than more obscure considerations like "Q Factor" or the angle of shoe-pedal contact. Kirby Palm has something to say on the matter, and it seems like a worthy enough final word.