KUOW's Tom Banse recently reported on Ductless Heat Pumps. You can listen to audio of the report here or read the transcript here.
He reports that some utilities will pay a rebate up to $1,500 for installing a ductless heat pump (and replacing less efficient heating systems, like electric baseboards). A 25% to 50% reduction in heating bills is the average, partially reflecting the amount of heat loss and inefficiency with ducts (estimates of heat loss in traditional ducted systems are 15-30%).
The Northwest Energy Efficiency Alliance reports that if about a million homes in Washington make the switch, that's an average of 440 megawatts of savings, equivalent to about one medium-sized coal plant. They say these are standard in Asia and Europe, and just now catching on in the United States.
Example ductless heat pump, $1,879 + installation. The appearance of the interior unit (lower) can be a drawback.
The homeowners in the report say that the total cost for their new heat pump was about $4,000, and will pay for itself in about 10 years. This technology may be more affordable in new construction or additions since no retrofit is required.
We still assert that the most efficient way to heat a home is with a hydronic system, where there is little heat loss, though these systems can be considerably more expensive and most feasible in new construction. Since you are heating materials (like the floors) not air, there is less heat loss when a door is opened. These systems also correlate nicely with the current emphasis on indoor air quality. Whole house fans create many air changes a day, which renders a system that heats just the air more inefficient.