In the talk, having reviewed a few chapters of the science-related history of MC simulations, we shall delve into this "real world". A prototypical example of these accurate yet flexible physical foundations of MC models is presented: scaled MOSFETs using Si, Ge, InP and In/sub 0.53/Ga/sub 0.47/As are simulated with a complete physical model. While at (relatively) large channel lengths, the small transport mass of III-V compound semiconductors gives them some performance advantage, at the shortest channel length their small density-of-states effective mass makes them "choke" (too few "channels" - a la Landauer - to carry current). Ge appears superior, but only on the chosen (111) surface orientations and ignoring band-to-band leakage issues. Additional examples - especially dealing with strained-Si devices, ballistic transport, and the meaning/relevance of the concept of "mobility" in small devices - are also given.