USB 3.0 promises a theoretical maximum rate of 5Gbps, meaning it's 10 times faster than USB 2.0. USB 3.0 is also full duplex, meaning it can upload and download simultaneously (it's bi-directional); USB 2.0 is only half duplex.
Put side by side with eSATA and FireWire 800, USB 3.0 is far superior. eSATA, an external connection that runs at the same speed as the internal SATA 1.0 bus, has a maximum theoretical of 3Gbps. This makes USB 3.0 faster than eSATA and about six times faster than FireWire 800 (full duplex at 800Mbps).
USB 3.0 also provides another advantage; while eSATA is faster than FireWire 800, unlike FireWire it cannot supply power. USB 3.0 has the advantage of being faster than both, even while supplying power.
Finally, USB 3.0 has improved power management, meaning that devices can move into idle, suspend and sleep states. This potentially means more battery life out of laptops and other battery-based USB-supporting devices like cameras and mobile phones.
Of course, there are other factors to consider; the FireWire 3200 standard is also in the works and promises to allow 3.2GHz speeds on existing FireWire 800 hardware. USB 2.0 generally doesn't meet its theoretical maximum throughput, due to its dependence on hardware and software configuration, where FireWire gets much closer.
It's hard to say whether USB 3.0's updated architecture will still use more CPU time than FireWire does.
