Very good topic to discuss in this economy. However, its not an easy task to develop a plan to systematically reduce the cost of IT.
I think cost should be linked to the architecture elements. In mapping costs to architectural elements and then aggregating them in various combinations (i.e. business process, capability etc) that are relevant to the business, IT can achieve a clear understanding of the costs. These architecture elements are the components that support a business capability.. you will then know how much is the operating cost to support a capability. Now, business can see the operating costs of a business capability/competency and can reduce the cost by focuing in those areas which need attention, ie, the area where business needs to close the performnace gap.