I agree with most everything that Darrel said. I also agree with myself. I wrote my reply because I keep seeing people saying that a 6 megapixel camera is superior or equivalent to 35 mm and medium format film at all enlargements. It just isn't.
Something I do wonder about medium format. I like shooting digital much more then film. If I had the money I would be putting a digital back on a medium format camera. This, to me, is the ultimate solution in the market today. I wonder if medium format digital backs came into line with the rest of the cost of medium format, we would continue to see the same ratio of medium format to "35 mm" format cameras used?
Something I'd like to add. If you can afford it get the D100, it really is great for most things. My personal rule of thumb is I will tell a client that I can always enlarge to 11"x14". It sure is a big step up from my 2.11 megapixel camera.