So why is Serial ATA so hot?
a) When faster drives are made, it has the theoretical bandwidth of 150MB/sec.
b) Bus master operation requires less CPU attention during transfers between the PCI Bus and system memory.
b) It uses thinner cabling (looks like a firewire cable that was run over by a steam roller). They potentially improve air flow and simplify installation.
c) With the right controller and adaptor/casing, you can run SATA drives externally and "hot swap" them.
Any down side?
Yes. You can only connect one drive per channel. You're allowed two drives per channel with conventional ATA and "lotza" drives per channel on FireWire 800.
Don't toss your Parallel ATA drives yet.
Wiebetech has already announced a SATA dock that lets you use conventional ATA drives as SATA drives externally. I found a few companies already offering IDE to SATA converters that should allow you to use your existing IDE/ATA drives with a SATA controller. Addonics makes a good one. Stay tuned, because I know a company working on a variation that will convert your internal ATA drives to Serial ATA.