Efficiency varies based on implementation, but it almost never rises above 50%.
"According to the U.S. Department of Energy, the efficiency of energy transfer for an induction cooker is 84%, versus 74% for a smooth-top non-induction electrical unit, for an approximate 10% saving in energy for the same amount of heat transfer.[20]" -- http://en.wikipedia.org/wiki/Induction_cooking#Efficiency_an...
"According to the U.S. Department of Energy, the efficiency of energy transfer for an induction cooker is 84%, versus 74% for a smooth-top non-induction electrical unit, for an approximate 10% saving in energy for the same amount of heat transfer.[20]" -- http://en.wikipedia.org/wiki/Induction_cooking#Efficiency_an...