It's a little tricky to explain to people the advantage of Thunderbolt over something like USB 3.0. If you look at base bandwidth, then at face value, there is little difference. Then add in the cost of active cables over Thunderbolt, the proprietary nature of the system, it's a very expensive version of firewire to most people and simply ignored. Why use TB when USB 3.0 is already universal and cheap?
I'm not an advocate of TB, but I can see the technical advantages of the system. First of all, in its simplest form, it's a PCIe cable; anything you can do with PCIe, you can do over TB. This means that TB can carry a USB 3.0 connection if you want it to. At the same time, it can carry DisplayPort, Ethernet, S/PDIF or even graphics... further still, it can carry all of these at the same time, limited of course by the total available bandwidth of the connection. It can also be daisy-chained. Mobile users got very excited over this, because it could mean that you could have a single cable that hooks up your laptop to a dock, which then provides all the I/O that you need, and possibly an external graphics card. Peak your interest?
So far though, all that's been released is a few NAS solutions, an incompatible monitor, and an incompatible Sony variation of TB... oh, and a very expensive dock by Belkin
But you can hook up NICs, audio and other things to a USB 3.0 port, why pay more for the same? Well... there is a more fundamental difference too. USB 3.0 is a protocol which is interpreted and then sent over PCIe, like SATA, this means that you introduce a middleman in the connection, and thus, latency is significantly increased. TB is PCIe, so there is no latency overhead (well, very little), so nearly the full bandwidth is available.
TB has its place, but because it's locked-in and misunderstood, it'll remain expensive and underutilised. Pretty much like Firewire - which in itself, was a niche but technically superior protocol to USB. There's a reason why a lot of older Pro-Audio gear used Firewire instead of USB... latency, signal quality and power filtering.