SATA is a newer technology that stands for Serial ATA I forgot what the ATA stands for... It replaces the regular IDE ports that connect your hard drive to the motherboard. Original technology allowed 100Mb transfer between the system & hard drive, but it was flawed because it shared the same bus channel as any other drive... SATAI was designed to increase speed between the two with dedicated lines between system & HD. The speed was increased to 1.5Gb/s or 150MB. SATAII operates at up to 3.0Gb/s or 300MB/s. It is also hot swappable, like USB.
The advantages are mainly the speed increase, dedicated bus (connected 2 drives does not hender performance like before with IDE).
As said, SATAII is UP to 3.0Giga bits a second. The actual speed may vary as needed.
Hard drive performance hasn't really increased by much for 10 years. The capacity of drives have though of course since 10 years ago. For Firewire drives, I would suggest using a SATA connection to keep the signal flowing fast through the SATA connection, to the firewire to the computer. There's still bottlenecks from using any hard drive IDE or SATA since the tech has been slow to increase. Top performance hard drives are like the WD 10k rpm raptor drives & seagates fall second place with their perpendicular drives. Of course I"m not including SCSI drives that fly at 15K RPM though....
I always stress, if your looking for performance on a computer, you can skimp on getting the best CPU, the best GPU, and 1gb memory, but your weakest link will always be the Hard Drive itself, so I suggest upping the speed on the hard drive before going out and purchasing a core 2 duo 6700 or quad core you know?
HOWEVER, most people of today don't need the extra x amount of speed that you get because it's not worth it. It's not that more expensive, but logic states that if you don't need it, don't get it.