I was taking MSM for RSI related pain/symptoms, but it is really nice for hair, skin, nails, etc.
In short, it is something that used to be in our soils, but is now depleted.
But our cells really like it.

[MSM, methylsulfonylmethane (METH-əl-sul-FON-il-METH-ane) provides sulfur, a vital building block of joints, cartilage, skin, hair and nails, and methyl groups, which support many vital biochemical processes in the body, including energy production. MSM is a naturally-occurring nutrient found in small amounts of many foods. As a dietary supplement, MSM is synthesized. When made correctly, it is identical to that found in nature. MSM can be taken alone or in combination with other joint health supplements, such as glucosamine and chondroitin.]

[Q: What effect will MSM have on my skin, hair, and nails?
A: Extensive anecdotal reports suggest that MSM supplementation improves the suppleness of skin and the shininess of hair and nails, which also become less prone to cracking and splitting.]
http://www.msmguide.com/