The current power carrying capacity of USB 3.0 connectors is limited today but by the Spring of 2012 a USB IF (USB trade group)a specification will be released that allows up to 100 W of power through a USB 3.0 cable.
In early 2012 the group expects to release a new prototype specification that will increase the power that USB cables can transport up to 100 W (20 V and 5 A).