  The goal of this paper is to highlight several issues which are most crucial
for the understanding of the ``metal-insulator transition'' in two dimensions.
We discuss some common problems in interpreting experimental results on high
mobility Si MOSFETs. We analyze concepts and methods used to determine the
critical density of electrons at the metal-insulator transition. In particular,
we discuss the origin of the temperature dependence of the resistivity and
reasons for this dependence to flatten out at some electron density in the
vicinity of the metal-insulator transition. This flattening has recently been
proposed to indicate a true quantum phase transition. We suggest an alternative
interpretation of this result and demonstrate the consistency of our
proposition with the experimental data. One of the main questions, which arise
in connection with the transition, is whether or not the metallic state is
qualitatively distinct from a conventional disordered Fermi liquid. We analyze
the arguments in favor of both affirmative and negative answers to this
question and conclude that the experimental results accumulated up-to-date do
not provide convincing evidence for the new state of matter characterized by a
metallic-like residual conductivity. We also discuss in details the measurement
and control of the electron temperature; these issues are crucial for
interpreting the low-temperature experimental data.
