Q: Is it the magnetic or electric components of light that get polarized? Since polarization filters light in all directions except one, the electric or magnetic field should be filtered, right?

A: Electromagnetic waves can be thought of as coupled oscillations of electric and magnetic fields, which oscillate perpendicularly, related by Maxwell equations, so that we can actually find the polarization of, say, the magnetic field from the polarization of the electric field. We usually only bother to specify one of them, and, by convention, we mean by "polarization" of an EM wave, that of the electric field.
