One of the really great things that will happen with the advent of SATA-2 is that external SATA will finally be *officially* supported with a physical connector. There are already some kits to take you external with SATA:
As far as speedy external storage goes, suddenly, Firewire will be... um... on the hot seat! When they start putting external SATA ports on computers along with the usual USB and Ethernet ports, Firewire will certainly begin to get pushed out of the general-purpose storage device universe and relegated mainly to the video/audio device connection universe. The USB universe will also ultimately be affected about as much as Firewire, but at least USB still has the vast keyboard, mouse, and whatnots markets sewn up.
External SATA DVD-+R/W, CD-R/W, and general purpose removable storage (floppy, Zip, M/O, tape, etc) should then finally be here along with SATA-2. The DVD and CD devices (both read-onlys and writers) should have fully native SATA controllers -- as in no more ATA-SATA bridge circuits.