What’s Thunderbolt? From Apple’s page on Thunderbolt:
Thunderbolt I/O technology gives you two channels on the same connector with 10 Gbps of throughput in both directions. That makes Thunderbolt ultrafast and ultraflexible. You can move data to and from peripherals up to 20 times faster than with USB 2.0 and up to 12 times faster than with FireWire 800. You also have more than enough bandwidth to daisy-chain multiple high-speed devices without using a hub or switch. For example, you can connect several high-performance external disks, a video capture device, and even a display to a single Thunderbolt chain while maintaining maximum throughput.
New cables and adapters for everyone! Rejoice!