Apple has always been somewhat on the forefront of new input/output interfaces on the Mac, going all the way back to SCSI on the Mac Plus, through FIrewire and USB. With the new Macbook Pro introduced today, they are continuing that trend with "Thunderbolt", a new high-speed input/output interface that allows you to link not just hard drives, but also displays and other peripherals.
It appears that Thunderbolt is Apple's competitor to USB 3.0, although they will probably support that on their computers, as well. It can move data at 10 Gbps, which is welcome news for anyone who deals with video and other large data applications.
You can read more about Thunderbolt at the Introducing Thunderbolt page at Apple.com.