Apparently i don't. The big toe nail on my right foot has been perpetually dead or gone for a number of years. It grows back, i do a long run, and it promptly dies again. It came off again a month after the Idaho Expedition race back in August. Looking down at my feet last night i realized that three of my other toes had grayish/black tinges on the nails and were only attached at the back and part way down the edges. They don't hurt. I don't notice any difference really. In fact, i can't really think of any reason why we even have toenails anymore - it seems that they are an evolutionary trait that we have simply outgrown in modern times. I mean i can still think of lots of times when i use my fingernails (picking out splinters, as a flat head screwdriver) and even my hair (keeps my noggin warm, impromptu floss substitute, deterrent to keep people from eating my guacamole), but seriously, when is the last time you used your toenails?