I'm running Raid 0 with an external drive for backup. They are both Seagate 7200RPM drives and the speed is between 200-243 MB/s both reading and writing.
The biggest plus is that it removes (lessens) the hard drive bottle neck. Anything writing to the hard drive has less time to wait.
If you want serious speed go for 2 SSDs (or 4 for 0+1) that will eliminate the long seek times as well.
