  A recent vast experimental and theoretical effort in manganites has shown
that the colossal magnetoresistance effect can be understood based on the
competition of charge-ordered and ferromagnetic phases. The general aspects of
the theoretical description appear to be valid for any compound with intrinsic
phase competition. In high temperature superconductors, recent experiments have
shown the existence of intrinsic inhomogeneities in many materials, revealing a
phenomenology quite similar to that of manganese oxides. Here, the results for
manganites are briefly reviewed with emphasis on the general aspects. In
addition, theoretical speculations are formulated in the context of Cu-oxides
by mere analogy with manganites. This includes a tentative explanation of the
spin-glass regime as a mixture of antiferromagnetic and superconducting
islands, the rationalization of the pseudogap temperature T* as a Griffiths
temperature where clusters start forming upon cooling, the prediction of
"colossal" effects in cuprates, and the observation that quenched disorder may
be far more relevant in Cu-oxides than previously anticipated.
