  This contribution briefly reviews some recent work demonstrating the partial
breakdown of the colloidal fluid <--> atomic fluid analogy. The success of
liquid state theory for atomic fluids stems in part from the van der Waals
picture, where steric interactions dominate the structure, and attractive
interactions can be added as a perturbation. For complex fluids described by
effective potentials, this picture may break down. In the first example
discussed, depletion potentials in non-additive hard-sphere mixtures are shown
to be surprisingly complex, leading to fluid structure and fluid-solid
transitions dominated by properties of the attractive potentials instead of by
the hard-cores. Many colloidal suspensions, and possibly globular proteins,
fall into this {\em energetic fluid} category. In the second example, the
coarse-graining of polymers leads to soft-core effective potentials and
associated {\em mean field fluid} behaviour distinguished by a breakdown of the
virial expansion, an equation of state that is nevertheless nearly linear in
density, and correlation functions well described by the random phase
approximation.
