  The ultra-high energy neutrino nucleon cross section grows at a surprising
rate with energy due to QCD effects in the target. Recent electroproduction
data allows an update of earlier predictions. We compare the results of our own
calculations with those of other groups, and critically review the foundation
and reliability of the calculations. The question of the `new physics'
potential of neutrino telescopes sensitive to the total cross section in
multi-PeV energy domain is considered. We point out a loophole in the arguments
which might be an important consideration in extrapolating the cross section to
extremely high energies.
