I recommand to read the blog post from Josh holmes about the importance of measuring ROI in our IT activities

few extracts :

• "But, if you're not measuring the ROI, how can you talk to the business about the possible ROI?"
• The cheapest feature is the one that you don't build in the first place
• If you can prove that you'll save 5 minute a day ..... This means that a save of $249.00, the ROI is 144% with a payback of 8.3 monthsHow much does it cost to run the software?
• In order to become a strategic partner to the business you have to prove that you are providing a great ROI for the business's investments in you. ... You can improve your projects ROI by reducing development costs, runtime costs, maintenance costs and by saving the company time, money and enabling new business.
• ...