More truth than hype in this case. The modern indoor lifestyle and diet are not very conducive to maintaining the requisite levels.
Vitamin D comes in many forms -- and not all are equal: http://en.wikipedia.org/wiki/Cholecalciferol
Vitamin D comes in many forms -- and not all are equal: http://en.wikipedia.org/wiki/Cholecalciferol
Also, D2 causes overdose effects pretty easily, but you can take big multiples of the "RDA" in D3 (I think 10,000 IU/day for months for vitamin D deficiency has been mentioned) for quite a while without overdosing.
That's actually a problem, as people can become accustomed to taking large doses and then not understand why problems are occurring when they start way down the road.