  For the two-dimensional electron system in silicon MOSFET's, the scaled
magnetoconductivity has been shown to exhibit critical behavior at finite
density $n_0$. Analysis of these magnetotransport experiments yields a product
$g^*m^*$ that diverges at this density (here $g^*$ is the interaction-enhanced
Land\'e $g$-factor and $m^*$ is the effective mass). This claim has been
disputed based on direct determinations of the $g^*m^*$ obtained from
Shubnikov-de Haas measurements. We briefly review these experiments, and
possible sources of the discrepancies.
