Hopefully the same as when you plug a Mac into another Mac via FireWire. (One of the Macs becomes the most expensive external HDD ever. This requires one Mac to reboot into the target disk mode. It would be nice if the same trick would be possible with Thunderbolt without rebooting.)
Something I really wanted is, when I connect my laptop to my home computer, my laptop can use the home computer's CPU, GPU and RAM and have an additional screen.
I believe Thunderbolt will make this dream true, since the Intel page mentioned "workstation performance expansion".
Snarky I know but I just couldn't help myself.