Heat pump is really just an air conditioner?

There is no difference when it comes to cooling your house, however it takes much less energy and costs far less to operate. You won't notice a difference in cooling capabilities, but you will notice a big difference in your utility bills, especially the heating aspects of the unit.

Heat pumps are a combination of AC and heating plants. If you had an AC system only (window units for example) you would also need to maintain a heating system. I agree with Annette on the expense but location has a great deal to do with heating cost. The farther north you are the less effecient a heat pump is so when outside air can't be used to create heat, there is an electric furnace which kicks in, and that's a very expensive utility.

gary999, Where I live in the midwest if you are all electric, the savings are substancial!! Regardless of how often the auxiliary furnace kicks on. Here it's gas that makes the difference. The house I built was all electric and my bills were cut in half or more. I have since purchased another house with a new gas furnace. When I installed the new heat pump and now have gas as my back up source for auxiliary heat the bills rose considerably. However my utilities are still $100 to $150 A MONTH cheaper than straight gas furnace in the winter months. So it's not really the low temperatures that determine the overall bill but the area you live in, and whether the gas or electricity is higher or lower and which of the two you have for your auxiliary back up. 

Excuse Me? Would you like to explain Bean?

Bean when you ask a question, the correct punctuation is a question mark. (?) Again, BUZZ off stupid. Why don't you go find something constructive to do with your time? Like sticking your finger up your butt, to see if you can locate your brain.

Put simply, a heat pump is an air conditioner that can go in reverse.  When you run an a/c system, the indoor coil absorbs the heat from the house as the air passes through the coil.  The heat is then released outside.  A heat pump absorbs the heat from the outside air and releases it indoors during the heating season.  Old-timers in the hvac business often used to call heat pumps "reverse-cycle A/C units.

ChuckBx2, Yup, basically that's all there is to it. Simple in it's design, but so  much more energy efficient than anything else. (other then a swamp cooler)

A heat pump is just a refrigerated air conditioner that cools a space when a switching device such as a thermostat is set for cooling. When the thermostat is set for heating the same air conditioner that was cooling reverses itself and produces warm air instead of cool air. The difference in a plain air conditioner and a heat pump is a couple of controls needed to make it reverse the flow. When cooling there is no savings between a plain air conditioner and a heat pump in the amount of electricity it uses.
When heating a heat pump won't heat your house unless you live in the desert but it dose reduce the cost of an electric heat coil, minimal.