How do you determine a measure for your IT Project?

As is true for any Six Sigma project, what do you measure and how do you determine if it is a good thing to measure? The essence of this question is determining what problem one is trying to fix and applying the Six Sigma principles to it.

The goal of measuring is to establish an objective baseline so that when the project is completed, the success criteria is clearly established as satisfied. So, the key is defining the problem well.

For IT, candidate measures are time (to derive a discrete result), effort (maybe, in terms of rework), when quanitifiable, ideally, dollars expended/saved, quality (when a standard objective measure for it can be established); all these, nothing different from the dimensions of project management. So, what's different? The operating word here is finding that objective measure that can be the basis of determining success of the project.