Maximum published everything you need to know about USB 3.0 over here. They take a look at all the changes compared to USB 2.0 and provide lots of photos.
Like the upgrade from USB 1.1 to 2.0, the new 3.0 connectors and cables will be physically and functionally compatible with hardware from the older specs. Of course, you won’t be able to maximize your bandwidth unless you’re using a USB 3.0 cable with Superspeed devices and ports, but at least plugging a 3.0 cable into a 2.0 port won’t blow up your PC. The spec’s compatibility lies in the design of the new connectors. USB 2.0 cables worked off of four lines – a pair for in/out data transfer, one line for power, and the last for grounding. USB 3.0 adds five new lines (the cable is noticeably thicker), but the new contacts sit parallel to the old ones on a different plane, as opposed to being adjacent to them. This means you’ll be able to differentiate between 2.0 and 3.0 cables just by looking at the ends.
USB 3.0 will offer a maximum transfer speed of 4.8Gbps (600MB/s) which is ten times faster than USB 2.0. Other interesting features are support for bi-directional data transfer, faster charging via USB thanks to a power output bump from about 100 milliamps to 900 milliamps and improved power efficiency.
The first USB 3.0 hardware for consumers is expected by early 2010.