  We examine the measured rates for the decays $D\to K^{(*)}\ell\nu$, $B\to
K^{(*)}\psi^{(\prime)}$ and $B\to K^*\gamma$ in a number of scenarios, in the
framework of the heavy quark effective theory. We attempt to find a scenario in
which all of these decays are described by a single set of form factors. Once
such a scenario is found, we make predictions for the rare decays $B\to
K^{(*)}\ell^+\ell^-$. While we find that many scenarios can provide adequate
descriptions of all the data, somewhat surprisingly, we observe that two
popular choices of form factors, namely monopolar forms and exponential forms,
exhibit some shortcomings, especially when confronted with polarization
observables. We predict $Br(\bar B^0\to \bar K^0\mu^+\mu^-)= 6.4\pm 1.0\times
10^{-7}$ and $Br(\bar B^0\to \bar K^{*0}\mu^+\mu^-)= 3.8\pm 1.3\times 10^{-6}$.
We also make predictions for polarization observables in these decays.
