I ran Tiger on my G5 Quad from a software concatenated RAID. I now run Leopard on a MacPro 2 x 3 GHz Dual Core Xeon from a software concatenated RAID. It creates no problems that I can detect. Of course, the G5 Quad had numerous other problems, and Leopard has had more problems than Apple ought to have allowed make to released software, but running the OS from a software RAID seems to have worked fine. YMMV. CR