http://www.jetsongreen.com/2009/10/cnt-regional-leed-case-study-illinois.html

The Center for Neighborhood Technology (CNT) conducted a post-occupancy study of 25 LEED commercial projects in Illinois and just published the first round of results from their research.  The Regional Green Building Case Study Project is one of the first post-occupancy studies to measure energy performance, greenhouse gases emissions, water use, transportation effects, construction and occupancy costs, health benefits, and occupancy comfort on a regional scale.  Although CNT found that some LEED projects perform better than others, they also determined that investing in energy efficiency pays off.  
More specifically, CNT found that LEED projects that obtained a higher number of EA Credit 1 points performed better than those that didn't.  In other words, projects that prioritized energy performance performed better than those that don't or than those that focused on other aspects of LEED certification.  
The study also found that since building performance -- a function of use, occupancy, operations, maintenance, and systems -- changes over time, a building's best benchmark is its own performance, as opposed to comparisons to other buildings or modeled predictions.  
As it goes, projects need to understand actual post-occupancy performance in actual operating conditions.  Projects can get this information through ongoing performance measurement and analysis.  And once provided with the information, owners can then set meaningful, realistic, achievable, and continuous improvement goals.
The Regional Green Building Case Study Project reinforces the USGBC's recent push for building performance with the Building Performance Initiative.  LEED 2009 projects have Minimum Program Requirements, of which, energy and water data sharing is mandatory (when not excepted).  While the USGBC will be using the information to inform future iterations of LEED, project teams can look at their own performance data to understand how to improve actual post-occupancy performance.  It's a step in the right direction.  
The Center for Neighborhood Technology will continue their research with a second phase later this fall.  You can read up on their first phase by downloading these files from source