One of the biggest problems DBAs run into is how to size and configure their disk I/O for optimum performance. While there are no magic solutions to this question, Microsoft has a great white paper on this subject all DBAs should read.
It is called "Predeployment I/O Best Practices" and is available at: http://www.microsoft.com/technet/prodtechnol/sql/bestpractice/pdpliobp.mspx
If you are in the process of specing out new hardware for a new SQL Server instance, you need to read this paper first.