As Dexter mentioned, there are a number of benefits to Vitamin D, such as a stronger immune system, faster healing for joint or bone injuries, less overall joint pain, improved mood and depression, etc. The aspect of the above mentioned article, which is worth paying attention to is the difference between the synthetic Vitamin D2 and natural Vitamin D3.
Yes, Big Pharma is promoting Vitamin D2 as a cure all, but it is misleading since the body does not assimilate D2 the way it does D3. The natural form of Vitamin D3, usually found in gelcaps, is absorbed by the body at least 10x better than D2. It is only by engineering a synthetic form that Big Pharma is able to market Vit D. As a result of the Vitamin D buzz, a number of well-meaning doctors (my mother's included) are prescribing Vitamin D2 to their patients. Rather outraged by the Dr's lack of knowledge, I told my mother to save her money and get the real deal, Vitamin D3.
Recently, I read an article which discussed the link between celiac disease and Vitamin D deficiency. Celiacs and other gluten sensitive people do not absorb Vitamin D correctly. This might be of particular interest to those who are recent Paleo converts and suffering from low Vitamin D levels. Dr. Davis discusses some aspects of this on www.theheartscanblog.com.
Regarding my own experience, I am a believer in the benefits of optimal Vitamin D levels. One year ago my Vit D level was 32. My alternative MD recommended 10,000 IU of Vitamin D3 per day. In addition to this, I started following a gluten free diet. Over the last year, my Vitamin D level has climbed to an optimal 68. My joint pain and mood has greatly improved and I have only had one cold in the last year...a record for me. At my Dr's suggestion, I have dropped to 5000 IU of Vitamin D3 per day as a maintenance dose.