At 06:12 PM 9/6/2011, Marius Strom wrote...
>If you go down this path, make sure it's either switchable or that you
>install a switch. 12V->5V convertors destroy a lot of power while
>sitting there idle.

Not anything reasonable. If using a cheap linear regulator like a 7805,
it will draw <10 mA quiescent current. They get inefficient only when
actually providing power, because they have to dissipate the
difference. I powered a couple of USB outlets with a LDO03C switcher,
so I could draw a full 1.5 A from each, and it runs <50 mA quiescent,
only a bit more than might be expected from a powered off car stereo.