Power grids : AC vs DC
Guy Allee at Intel Research wrote about this topic last year -- DC - An idea whose time has come and gone? -- in support of a 380VDC grid, with the following bullet points:


  
  7% Energy Savings vs. High-Efficiency 415VAC; 28% vs Current
  Typical 208VAC
  15% Less Capital Cost
  15% fewer PSU components
  33% Datacenter Space Savings
  200% Reliability Improvement, which goes to 1000% if you directly connect
  the battery bus
  Elimination of harmonics and inherently immune to other AC power
  quality issues
  Natural affinity to alternate energy generation (Photovoltaic, and wind are
  ~400Vdc internally, and you actually
  lose energy &amp; efficiency when you are
  forced to convert to AC)
  


He added in the comments:


  We very deliberately picked 380Vdc
  because you want to get to as high a
  voltage as you can afford for
  efficiency. At the same time this
  standard is targeting Low Voltage
  applications only (&lt;600V). We would
  have gone higher, but there are
  structural cost barriers at 400Vdc and
  420Vdc. At 380Vdc we stay with the
  same volume parts ratings that AC is
  using and get the volume cost benefits
  of piggybacking on the bulk of current
  AC power supply component volumes. I’m
  sure you can also appreciate the
  significant cost adders that +/-340Vdc
  has on the personal safety equipment,
  which is why the standard allows for a
  cost-effective +/-190Vdc distribution.
  Thus we have the highest efficiency
  yet cost effective standard. And with
  the affinity among other industries,
  PV, wind, electric vehicles, and
  lighting, the volume economics seem
  compelling.


He also mentions the idea of a mixed distribution of both AC and DC within a building (e.g. data centers). For more on that initiative, see the EMerge Alliance website: http://www.emergealliance.org.