Apple did not invent USB, Intel did.
Designer Ajay Bhatt, Intel
Designed January 1996
Manufacturer Intel, Compaq, Microsoft, NEC, Digital Equipment Corporation, IBM, Nortel
Superseded Serial port, Parallel port, Game port, Apple Desktop Bus, PS/2 connector
Apple is not even on the Board at the USB consortium: www.usb.org
There will be room for both but as you said the consumers will have the final say.
The motherboards I see and buy have many times more USB ports than FireWire due to the formers high take-up rate and low cost.
On the flip-side (as a hardware guy) FireWire does not use as much CPU time as USB.
IMHO - Thunderbolt (LightPeak is better) will be limited to the Mac domain and there will be some PCIe Add-On cards for PCs.
Then don't buy an external HD without either FibreChannel or 10Gb ethernet fabric.
You starting to feel the pain yet?
"Thunderbolt" (really lame name) is nothing more than 10Gb ethernet with a differing protocol. With that said, 10Gb transceivers (optical in particular) are not yet commodity priced interfaces so it will start off slow and more than likely be replaced at the point of "final take off" by 100Gb ethernet.
10GBPS serdes probably fits better into their process roadmap, where 5GBPS (USB) either leaves too much performance on the table or fizzles out too soon. Apple invented USB, so they surely looked long and hard at the tradeoffs between USB and Thunderbolt.
The controller chip is required on both side, in transmitter - a notebook and in receiver - a peripheral. Also, as written here, TB is expanding PCIe to an external box so if you want to put any device on this extend PCIe bus one would need PCIe to xyz converter silicon - for example PCIe to Sata for sata drive. With today's semiconductor technology all these (TB controller plus xyz peripherals) could be integrated in a low cost solution but it does not exist today. So I would say there were will be players like Apple who will use this technology but any mass adaptation is two to three years away. Oh by the way the DP is only 1.1 not 1.2!!
The new SSD external HDs using SandForce 2 controllers are pushing 400MB+/sec speed that USB 3.0 is unable to support (400MB is theoretical after protocol overhead). Will USB 4.0 come out in 2012-13 to support the next generation SSD drives? I'm buying a new Macbook Pro because of the fact it supports Thunderbolt so I can use it with the new SSDs and not have an interface bottleneck.
Higher speed may finally turn out new applications, especially from some companies like Apple. Without knowing the price tag however really puts some uncertainty on how well the market can accept this new technology. But Intel+Apple seems is a good reason why people can keep watching at.