VideoMaker has a quick little breakdown on the differences between USB 3 (which should be getting a speed improvement to 10Gbps from 4.28Gbps) and Thunberbolt, which is is currently 10Gbps, but with optical cables can go up to 20Gbps in the future and can carry video and more power (though I don’t see how that will be possible with optical).
I have a feeling this will be like Firewire and USB, where USB will eventually win as it is cheaper and backwards compatible, even if Thunderbolt is superior in some way.