Currently, two broad questions are driving observational and
theoretical studies of the low-redshift intergalactic medium: (1) Are
the missing baryons located in the "warm-hot" intergalactic medium
(WHIM) at the present epoch?  Hydrodynamic cosmological simulations
predict that as the universe evolves and large-scale structures grow,
intergalactic gas accretes into increasingly deeper potential wells,
and a substantial amount of intergalactic material is shock heated. By
z = 0, the simulations predict that 20 - 50% of the baryons are shock
heated to temperatures of 1e5 - 1e7 K, the so-called WHIM.  This is
purported to be a robust prediction from these popular simulations,
but is there any *observational* evidence of the WHIM?  (2) How do
galaxies affect their surroundings, and how do surroundings affect
their galaxies?  Processes grouped under the rubric of "feedback"
(e.g., supernova- or AGN-driven outflows) are often invoked to solve
problems in galaxy evolution, but observational constraints on
feedback are still quite limited.  Conversely, theorists have
suggested that gas accretion is more complex than previously thought
and occurs in "cold" and "hot" flavors.
To provide observational constraints relevant to these topics, we
have been conducting a high-resolution spectroscopic study of the
low-redshift IGM using QSO absorption lines.  This talk will summarize
several new results from this survey, with a focus on QSO absorption
systems detected in the O VI doublet.  The O VI doublet is frequently
detected in low-z QSO spectra, but it will be shown that the absorbers
have some surprising properties, e.g., the gas is often cooler than
expected (T << 1.0e5 K), sometimes quite enriched with metals (in some
cases approaching solar metallicity), and rather far from luminous
galaxies.  The speaker will wave his hands furiously to deal with
these findings but will conclude by demanding much more telescope time
to really understand the role played by the IGM in galaxy evolution.