To the best of my knowledge there's no separate electric heater for the coolant of the inverter/MGs — after all, the inverter and MGs heat up all by themselves due to conversion losses that occur in their operation! This coolant is circulated by an electric pump through its own radiator. This is an entirely separate cooling system from that of the ICE. The A/C cooling system is also separate from the ICE, also with its own electric pump and radiator. Any additional heating will use energy that ultimately comes from the gasoline (maybe via the battery). A low-power block heater would probably be a more energy-efficient way (than running the ICE on gasoline) to get it up to operating temperature quickly, and it's the component that most needs this help in order to operate efficiently. So, a block heater may make sense in really cold climates. I don't think southern Ontario counts as really cold.

Stan

Added note (2006-12-05): I checked the circuit diagrams, and there is no electric heater for either the inverter/MGs' cooling system or the A/C cooling system. The electric water pumps and associated radiators and cooling fans for these systems are thermostatically controlled, so their fluid should heat up fairly quickly from normal usage.