I like to keep my left hand nails super short. Before I really started to play aggressively, I could manage with them right up to the tips of my fingers -- but now that I'm looking for a louder and more distinct finger-style sound, they need to be really short. Many women get manicures -- but not me. It's just not worth it.
The irony, is that the act of playing makes your nails grow faster, so if you want to keep them this short, you have to pay attention to them every few days. If I let mine go too long, I will cut them -- but I prefer to file with a medium grit emery board. You aren't doing your strings or your neck any big favors when you clip -- as the edges are rough and scratchy. I always make sure to have an emery board in my case. You can find them in a four inch length. Buy a pack and stash one in your case, with your music, etc. I don't like metal files at all -- well, except as a weapon.
Since I like to play double-stops, I'm getting a good set of callouses on the sides of my index finger. If the callouses get nicked or start to flake, I file them with my emery board too.
You can always tell if a female is serious musician by looking at her left hand (well, nails in general for the guitar -- but especially the left hand). If I can see any white under the nails on the left, I know they are too long. Taking care of the right hand is a lot more involved, so that will come next...

