I've just recently started working in a small computer shop, and everyone there swears by SCSI hard drives. The newer drives have a transfer rate of 133 mb's a second and a latency of 2.7ms. They are perfect for video editing and movie playback, they are a little more trouble to install, but from what I've seen, the benefits outway the extra steps to set the drive up. And they are designed to be used 24 hours a day unlike an IDE drive that is designed to be used up to 10 hours a day.
By using a SCSI controller, it takes some of the load off of the CPU.
Even the older SCSI drives outperform most new IDE drives.
And a word of warning, stay away from WD IDE drives, my boss says that he has always had a hard time returning them, and as for quality they are on the lower rung. AS for my personal experience, I've just recently had a three year old WD drive fail.
I recently switched my home system over to two SCSI Hard drives, and it was fairly easy, now if I can find a good SCSI CDRW, I'll be set.
Just an alternative view point, not meant to start a flame fest.