  We provide a generic but physically clear discussion of the clustering
properties of dark energy models. We explicitly show that in quintessence-type
models the dark energy fluctuations, on scales smaller than the Hubble radius,
are of the order of the perturbations to the Newtonian gravitational potential,
hence necessarily small on cosmological scales. Moreover, comparable
fluctuations are associated with different gauge choices. We also demonstrate
that the often used homogeneous approximation is unrealistic, and that the
so-called dark energy mutation is a trivial artifact of an effective, single
fluid description. Finally, we discuss the particular case where the dark
energy fluid is coupled to dark matter.
