Group, ROI is a good tool, in many ways, if taken in the right context and used in a responsible manner.
Let's expand our discussion a bit to evaluation tools in general. Our question asks about ROI, but what other tools would you chuck into the toolbox if you were headed into a performance evaluation? Would it matter to you what level of the organization the employee was at? How might your tool selection differ for an upper level versus lower level employee? Group, your thoughts?