I use my D100 for most everything. However, I really can tell the difference. It is just a matter of whether it it good enough. That is subjective.
All these posts seem to miss a key point. They are talking about prints in isolation. Take a picture of the same scene with a D100 and scan a medium format print of the scene, for example a landscape with lots of detail. Now see if people like the medium format better.
Note: As the dissenter I want to make it clear that I love the D100. I think it is good enough; the composition etc. matter so much more then the resolution I don't think twice about using it. However, if I were buying a print of something with lots of detail I would buy the larger format as others for years have.