The 1-amp rated Samsung AC charger supplied with my Galaxy Nexus has pins D- and D+ shorted.

The cheap china car charger I got from DX has proper resistor networks to signal 500mA max per port (2 USB ports). I just now hacked it, adding 200ohms across D- D+, to trick my phone into charging at (up to) 1amp from it, instead of trickle charging as it normally would.