I also believe that it depends on ones environment. At a previous employer, the principal database servers reside on blade servers attached to a high performance SAN. The mirror servers are stand-alone rack servers with DASD. This setup provides more than enough horse power and availability for the LOB (Line of Business) applications. HR, Finance, SIS (not to be confused with SSIS) each have their own servers and the 32 GB of RAM on the blade servers is more than enough to support the applications now and in the foreseeable future.