Not sure if this was already discussed here, but it seems that new cars will eventually be operated on a 42-volt system:
http://www.caraudiomag.com/specialfeatures/0307cae_42volt/
http://www.batteriesdigest.com/42_volt.htm
http://www.memagazine.org/backissues/apr02/features/fortytwo/fortytwo.html