Wow, WTF. I can't imagine keeping track of all those, and can only wonder if he's overdosing on any of them. Doesn't it wreak havoc with your digestive system?
<Rambling ahead> That said, I do take vitamin D supplements since I'm not spending as much time outside as I used to(I miss the lazy days of summer in university), and thus not getting as much Vitamin D. Last year my doctor told me that my Vitamin D levels were low and prescribed a once-a-week dosage of 10,000IUs of it for a couple months. After that I started consuming 2,000IUs / day, 4-6 days per week. The consensus is that the minimum amount is 400IUs, so I do more simply because I know I'm inclined to miss a day here and there.
I suppose time will tell just how effective Vitamin D really is, but I'm fairly certain that I'm helping myself by taking it. Besides, an ounce of prevention's worth a pound of cure, and each $5 bottle of the stuff lasts me several months.