[Zathras]

We have a closed loop system and love it. Located in Minnesota so the heating is more important to us than the cooling.
Payback for us is between 4-7 years.
From Feb - spring last year our gas furnace back up was not used (do to the hookup not being turned on) and while it got a little chilly (58-60) nothing unbearable. It handled all the heating until the outside temp got below about 0-5 below zero.
Our house also has highly efficient insulation. With less insulation the geo system would need to do more work so your results will vary.
If you go with a closed loop and have the space for a horizontal trench it is much cheaper than digging the vertical holes. You need about 100ft trench for each ton of heating/cooling.
If you have moist sandy soil, that holds the heat better than dry, clay soil so you will get better results.
The efficiency the second year is turning out to be better than the efficiency the first year. Not sure if that will hold through the entire winter, but we shall see.
Our system heats our infloor radiant system, water heater and helps warm and cool the A-coil in our furnace so when it is needed it takes a little less energy.

Also check with your local power company. Ours agreed to give us off-peak pricing all day for using a dual fuel system (heating, water heater, cooling all use geothermal primarily and only draw electricity/gas when geo is insufficient). So we end up paying 5c/Kwh for those as well as the electric pump.

Our builder worked with the contractor so I can't tell you much about how easy it is to find one. However, make sure they have done it before, preferably a number of times.