I found this website
Green Data Center Blog: Who are the Energy Hogs in Data Centers? where the author is talking about energy hogs in the datacenter arena. It would be interesting to know.
I would think those utilizing some form of virtualization technology would hopefully not be on the list.

Right now there is a huge push to spend less on resources, and datacenter costs, as well as overal IT expenditures.
We in the IT sector have the ability to directly affect not only our end costs and bottom line, but the energy issue and crisis that our planet is facing today.
Here is an  article [...]