The Elusive Technology ROI

Why is it so hard to measure the ROI on technology? How might we make some sense of the controversy surrounding IT\´s value? Should we let our vendors tell us what the ROI of a new technology might be at our company? Do we have all of the facts to make a legitimate prediction of ROI prior to undertaking a project, or does the ROI analysis require making a lot of "glass-half-full" conjectures? Information systems managers continually struggle to evaluate potential projects and establish the bottom-line effect of IT investments. There must be an easier way to perform this important task.