Thunderbolt Port + External Display + Other Devices
Thunderbolt is different than other connectors in that there are two 10 Gbps signals multiplexed on one physical connector/cable assembly. The DisplayPort signal will go down the chain of devices uninterrupted so the full DP bandwidth will get to the monitor that will ultimately end up at the end of the device chain. Of course new display hardware could be released to add a hub / further Thunderbolt connections - but existing DP monitors should work as described.

All the rest of the devices will share in the PCIe bandwidth - sort of like how existing system boards have multiple PCI slots operating at full speed. Until vendors start shipping real devices with hubs and connectors - we are limited to speculation and browsing the engineering/marketing materials released by Intel and Apple.

From what I've read, the initial devices will be like FireWire devices - two Thunderbolt ports per device - one to the computer and one for the next device to connect down the chain. The bi-directional, hot-pluggable, dual-channel cables with substantial bus power means the best aspects of FireWire could be commonplace as a much more powerful standard for years to come.