Just wanted to say thanks for this. I'm going to definitely cite this as a reference for some of my clients that use the BSD platform.
Also, you might want to check out this RAID Calculator (http://www.icc-usa.com/store/pc/viewContent.asp?idpage=7) as well. It seems a bit more complete and explains all of the different RAID settings, use cases, etc.
(in the spirit of full disclosure, someone at our parent company created it, but I just send it to clients when necessary)
P.S. I recently took over ServerProblemsSolved.com (http://www.serverproblemssolved.com) , and we're working on a RAID article, so I will make sure to cite this for the BSD users. Thanks again!