** Update 2014 **
I am transitioning away from RAID arrays (and no longer use LVM). For smaller amounts of data I am migrating to btrfs (RAID 10 or RAID 6 and larger amounts of data a cluster (using ceph or swift) is usually the answer.
** End Update **

I am a big fan of RAID arrays and I use them everywhere. After having been bitten by failed, end of life hardware devices, I have become a fan of the software RAID. In particular I am quite happy with the Linux software RAID capabilities when paired with the Logical Volume Manager (LVM).

First, I create some partitions on the drives I want to use, in my case, I have four 1TB drives that I am putting into an array. You do not need to create partitions as Linux can use the whole drive as it is, where you may have issues is if you plug the drive into a computer that does not support Linux RAID, it may prompt you to format what appears to be a blank drive. If you use partitions, at least the OS will see an unsupported partition and probably do nothing. This is not a big deal but it can help to prevent you from shooting yourself in the foot, especially when you have more than a few drives on the workbench and more than one OS in daily use.