A quote from the linked article, "Unlike ordinary heating and cooling systems, geothermal HVAC systems do not burn fossil fuel to generate heat; they simply transfer heat to and from the earth. Typically, electric power is used only to operate the unit’s fan, compressor, and pump."
This is very misleading, as a typical geothermal system works just like any other heat pump (air conditioner) except the heat/cold sink is the earth rather than the atmosphere. There is little question that geothermal saves energy, but it is not an energy production system, so it is not renewable energy. Essentially, a geothermal system increases the efficiency of a heat pump by having the heat sink at a warmer temperature in winter and cooler in summer, than it would be in an air sourced system. In some exceptional situations, where there is geothermally heated hot water available (like in parts of Iceland, and some places in the US) then the geothermal system actually supplies the energy, and would legitimately be called a renewable energy source, but this is not the case in most geothermal systems.
The quotes I have seen for geothermal systems have been very high, often 10 times what an air sourced heat pump/air conditioner would cost.
The longevity of the in ground heat exchangers, which generally represent the majority of the cost of the system, is the subject of much debate. Though it is entirely possible that an undisturbed heat exchanger could last almost indefinitely, often their is ground movement (due to tree roots, water movement, settling, or even seismic activity) that breaks the pipes.
Another quote, "Standard air-source HVAC systems cost around $3,000 per ton of heating or cooling capacity, during new construction (homes usually use between one and five tons). Geothermal HVAC systems start at about $5,000 per ton, and can go as high as $8,000 or $9,000 per ton."
I built a house recently and paid about $500 per ton (two 5 ton and one 3 ton unit) including the 90+% gas furnaces. Even if I include the installation cost for the ducts, registers, etc. (things that would have been required with or without geothermal) the cost was about $1000 per ton. Perhaps the cost for HVAC has gone up some since my house was built but not enough to reach $3000 per ton.