An internal chargeback process can save lots of money and get you fired because this approach is the one most fraught with political peril.

Without a chargeback mechanism, business units tend to look upon IT as a giant free toystore. Put one in place and those same business units feel free to go to the outside to get more competitive technology pricing, and IT loses control and becomes marginalized. If your company is going to consider this, there are ways to achieve both goals: making the business units accountable and maintaining central technology architectural control.

Internal IT must be competitive with external service providers. Periodic benchmarking exercises are key. Don't underestimate the substantial resources needed to effectively administer chargeback mechanisms to ensure that business units have all the information they need and no one feels at a disadvantage. IT must have a clear understanding of all costs and manage the demand appropriately. Use client satisfaction surveys and service level agreements (a good idea no matter what the circumstances) and always show a balance between costs and benefits.