I don't know anything about the Hybrid Camry, but I know enough about the synergy system. I own a 2003 Toyota Prius and am super happy with it.
The basic gist of the hybrid system is that you've got two motors delivering power to the wheels, one electric and one gas. The amount of power coming from the respective motors, and the mix of power from both, is determined by acceleration, steady speed, terrain, or in summary demand for power. At low speeds (up to 35 mph on flat terrain) the vehicle is capable of running completely on the electric motor, thus maximizing fuel economy. At stop lights and stop signs the gas motor automatically shuts down and re-engages once a certain speed or power demand has been reached.
Maximum fuel efficiency is achieved in hybrid vehicles when the hybrid battery system (not the same as the starter battery) is fully charged. Charging is typically a function of two things: regenerative braking, and low power demand coasting. During braking, the electric motor on hybrid vehicles runs in reverse and acts as a generator, sending power to the battery system for storage. More braking = more charging = more electrical power available for the electric motor = better fuel economy. This is why hybrids do NOT get outstanding (though still better than most) fuel economy on short trips--simply not enough time to fully charge the hybrid system. I have found that I get maximum fuel economy on trips of greater than 15 minutes drive time with a mix of stop and go and steady speed driving over 35 mph.
To address this issue independent researchers and engineers are designing hybrids that can be plugged in while not in use, which will enable hybrid battery systems to remain fully charged at all times. The vehicles will not NEED to be plugged in, but folks looking for greater fuel economy (up to 100 mpg) may do so at their convenience.
One thing folks never talk about with respect to hybrids is that they offer significant emissions improvements over traditional vehicles. Most hybrids qualify for the either zero emissions or partial zero emissions standard, which is why most states provide tax credits to new owners.
Hope this helps.
