Without a doubt, if you add up all of the feet walking up stairs, chalk screeching across chalkboards (do they still have those?), sliding doors sliding, paper being crumpled up, people scratching themselves, and various and sundry other folderol, there is a lot of energy wasted in the world. The big hairy but in all of this is 'Can this energy be recovered effectively?' Unfortunately, as people are finding out, often the answer is, 'No, it cannot.' Efficiency is the big bugaboo in all such schemes. We don't have a machine or a process where we can round up a bunch of stray joules of energy, collect them, and crank out kilowatts of power out the back end. In fact, it would probably take more energy to collect these stray joules in the first place than what would be obtained in useful electrical output.
There is a concept in thermodynamics called 'availability', or to use a more modern term, 'exergy'. This concept deals roughly with how readily a given quantity of energy can be turned into useful work, and it incorporates other thermodynamic concepts like 'Carnot efficiency'.
http://en.wikipedia.org/wiki/Exergy
To give an example, in the summertime, tropical bodies of water, like the Gulf of Mexico or the Caribbean Sea, are crammed with gigajoules and terajoules of energy from the sun trapped by the water. Hurricanes and other cyclones feed off this energy after they form to sustain the high winds characteristic of these storms.
There is undoubtedly a large amount of power which can be generated from warm water. Why hasn't man been able to harness such energy? The answer lies partly in the fact that all of our most efficient methods of conversion of energy into work involve having the energy flow from a high-temperature source to a lower-temperature source. The greater the temperature difference, the greater the efficiency of the conversion of energy to work.
There have been proposed ocean thermal energy conversion projects which would pump hot water from the surface into a specially-designed heat engine, which would convert the thermal energy into work.
http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion
Because of the low temperature differentials involved, such conversion has an efficiency of about 1% to 3%, compared to conventional power plants which have thermal efficiencies of from 40% to 50%. Thus, it takes a very large ocean thermal energy plant to replace one conventional power plant, on the order of ten times as big. Although you don't have to buy fuel for the ocean plant, it will take much longer for the ocean plant to pay for itself than the conventional plant.
