Data Center Managers have become much more focused on cooling efficiency in the past 18 months. The industry has more or less standardized on using PUE to provide the relative efficiency of a data center. For example, the new Energy Star designation will be largely based PUE. Having this guideline has created a methodology to determine how efficient a site as a baseline to compare to industry averages.
Switching out older servers for newer more efficient models can help but that is not a realistic budget option at most locations right now. Improving cooling efficiency is the biggest opportunity to cut power consumption.