  We discuss two aspects of f(R) theories of gravity in metric formalism. We
first study the reasons to introduce a scalar-tensor representation for these
theories and the behavior of this representation in the limit to General
Relativity, f(R)--> R. We find that the scalar-tensor representation is well
behaved even in this limit. Then we work out the exact equations for
spherically symmetric sources using the original f(R) representation, solve the
linearized equations, and compare our results with recent calculations of the
literature. We observe that the linearized solutions are strongly affected by
the cosmic evolution, which makes very unlikely that the cosmic speedup be due
to f(R) models with correcting terms relevant at low curvatures.
