Essentially, Thunderbolt multiplexes two full-duplex PCI Express channels with DisplayPort video to expand the I/O capabilities of a computer. But Thunderbolt has some major points against it when it comes to enterprise storage use: It is fundamentally a personal computer interconnect, intended for docking stations, not data centers.
Although prototypes and future versions use compact fiber optic connectors (thus the "Light Peak" name), the production version of Thunderbolt uses electrical signals over a copper wire. That wire was a surprise: It rides along on Apple's Mini DisplayPort cabling spec, duplexing PCI Express data with digital video. Thunderbolt includes two full-duplex PCI Express channels, for a total of 40G bps of bi-directional throughput over a thin cable up to 3 meters in length.
Thunderbolt extends the host computer's PCI Express bus outside the physical chassis, allowing external devices to appear as though they are inside the case. Each peripheral will thus need its own Intel Thunderbolt de-multiplexer and PCI controller. Since Thunderbolt can flexibly manage the two included PCI Express channels, Intel promises high performance regardless of the other workloads sharing the connection.
In the future, we will likely see Thunderbolt hubs, optical repeaters and docking stations appear to increase the range and flexibility of this new I/O network.