This example of using the waste heat from a data centre to warm nearby building is a good illustration of the potential to be realized by linking energy flows across several buildings:
Any laptop user will know that even the most casual of Twittering with a computer resting on your knees can get uncomfortably hot -- so imagine the vast amount of heat that a massive IT data centre kicks out. Now telecommunications company Telehouse Europe is planning to capture that and pipe it to nearby homes and businesses.
(Via Worldchanging.)