Shock, horror! Anandtech did a bunch of research with Western Digital's high performance SATA drives, and discovered that RAID 0 offers somewhere between a slowdown, and a minor increase in speed when used on a desktop machine.
Generally the increase was between 2-4%, except for Far Cry, which showed a decrease in performance when loading from a RAID 0 array! Unreal Tournament showed no difference between single drive and RAID 0.
So, to sum up, RAID 0 offers advantages for disk benchmark programs, but makes fairly little different to real world programs.
You can read the article
here