Disk performance seems to have traditionally been measured in how many acronyms you could list as present in a solution. In filling the need for better metrics on storage performance, IOPS has become a commonplace term in determining shared storage capabilities.
Check out this latest podcast where VKernel's Brad Bonn and Jonathan Klick discuss the benefits and pitfalls of focusing on IOPS, and how storage I/O is an often over-simplified topic.