GamePC has completed a comparison of onboard "software" RAID controllers versus add-in hardware-based controllers.  Is the performance difference worth the added cost?  Read on to find out:

While RAID-5 controllers are dropping in price, becoming more readily available and arrays are getting easier to setup, RAID-5 still is a bit out of range for the typical home user. None of the three RAID-5 controllers provided us with an utterly seamless RAID-5 experience that we were looking for. Some have setup issues, some have software issues, and some have performance issues. Nobody is a clear winner here, although each controller does have advantages.