  The simplest extension of the standard model involves adding a scalar
doublet--the so-called two-Higgs model. In general, the additional scalar will
mediate tree-level flavor-changing neutral currents. Although one can
arbitrarily impose a discrete symmetry to avoid these, it isn't necessary to do
so; reasonable assumptions about the size of the flavor-changing couplings can
make them sufficiently small as to avoid problems in the kaon sector. However,
these same assumptions give much larger effects in the third-family case. We
discuss the model, the "reasonable assumptions" on the size of the couplings,
and examine phenomenological bounds on the couplings, showing that the most
promising signatures are from $B_s --> \mu\tau$, $\mu --> e\gamma$, etc. We
then include the newest result which shows potentially significant effects on
the anomalous magnetic moment of the muon.
