* SATA is point-to-point, so each drive gets this bandwidth. USB is a tree, bandwidth is arbitrated between devices.
* SATA 2 came into commercial use relatively shortly after introduction. I haven't seen any USB 3.0 devices yet (host adapters/motherboards or nodes) and driver support during the USB 1.1->2.0 transition was pretty bad. Apparently, Windows users will need to wait for Microsoft to release host controller drivers. I suspect they'll only be available for Windows 7. No idea when OSX will support it, presumably Linux will be first, assuming the spec is made available to the developers.