Recent developments of the VITESS Monte Carlo software package for simulation of neutron scattering instruments allow for the computation of neutronic systems of very complex geometry. For example, the module 'supermirror ensemble' simulates a number of supermirror plane sections in any geometry, including spin dependent reflectivity and absorption. This module was intensively used in the optimisation of the bi-spectral extraction system for the new guide hall of BENSC at HMI. It was also used for simulations of beam splitter polarizing cavities at BENSC. Another example is the module 'Fermi chopper' which simulates real three-dimensional slit packages with no analytic approximations. It will also be shown that this latter module has been very successfully bench-marked with HET/ISIS experimental data and is consistent with analytic theory. Finally, we will present a sophisticated Monte Carlo simulation study of a time-focused pulsed source crystal analyzer spectrometer prototype, which is planned to be realized in a test at IPNS. A short account will be given of this example illustrating the high performance of the VITESS simulation package.