I knew hair and nails are dead matter, but from the brief study I did, found quite a bit of interesting tidbits.
From this site at Total Beauty this tidbit:
"Iron: Brittle nails can be a sign of an iron deficiency. Look for chelated iron supplements or consume more nuts, lean red meat and green, leafy vegetables. These all contain essential vitamins for nails."
A few other sites I thought beneficial are:
Livestrong
Ehow
Wikihow
As a note, personally, I prefer to NOT apply items that are meant to harden the nails.
Nail Art 101 had this to offer on cuticles when I went searching for more information on massaging!
"First and foremost, try to avoid cutting your cuticles. It makes you suceptible to infections and fungus and can leave you with ragged looking nails. Use a cuticle remover instead. Gently push them back with an orange stick or cuticle pusher, then apply the cuticle remover."
And everyone's favorite Ehow - lol: