RAID is for combining two or more physical drives into a single logical drive. The ATA bus on the QS should be 66, so boosting it to 100 or 133 will speed things up a bit if your drives are ATA100. Hard to say exactly how much you will notice the diference. If you do alot of video work, or anything requiring frequent disk access you will likely appreciate any boost you get, but otherwise it should make apps launch a bit quicker. Should boot a little faster too. Whether the increase would justify $100 is really down to how you use it. Having said that you can transfer the ATA card when you eventually upgrade the whole machine to a newer one, so it has potential to be useful for a while to come.