The 3200 sq ft farm house (40x40 2 story, full basmt and walkup attic not heated or cooled)  built 1908 with new windows and foam insulation and new foil backed insulation board under vinyl siding all in 2000:  has a dual heat-a/c unit and with LP heat backup for emergency, extreme low temps, like below 10 F with high winds need to be able to supplement, especially with little snow cover. 
  Shed has one heat unit and one heat-a/c blower unit.  Heated water is sent to two 100 gal hot water heaters for storage reserve.  They can be used as backup heat source, but we've never wired them up to electric, yet...  The blower is necessary for the a/c, but also nice for iced and snow covered equipment.  Shed has 3 ceiling fans only used in winter. Installed system in 2009 when shed was built.  The attached 2-truck garage on shed is floor heated also. 
  Lines in field serve house and shed, pumps run as needed where needed.  9 trenches either 300 or 350 ft long with two layers of 2" plastic.  so one set at roughly 4 1/2 ft and the other at 6 ft, plus the main run to the shed is another 100 ft.  We wanted to do the trenching ourselves, but installer wouldn't warranty the system unless they controlled the whole project.   Our install was late fall of 2009, and actually didn't fill and purge the system until March of 2010.  All of our problems have been electrical related, first couple under warranty, but likely caused by lightning.  Last two service calls were error codes on the house thermostat, requiring manual system reset.  So, you leave the house at 8 am, temp is 73 inside and come back for lunch and it's 80 degrees.  So, you turn it off and turn it on, and by 3 pm it is back down to 73.  Remember cooling is more effecient transfer than heating.  It's been fine now for 3 weeks.

Our installer, from Oglesby, IL.  John’s Service and Sales is one of only 4 companies in the entire state of Illinois with an IGSHPA Certified Geothermal Designer on staff. John’s has designed, from the ground up, several geothermal systems from 3 to 130 ton. John’s has designed geothermal projects utilizing all types of geothermal systems including ground and pond loops, open and closed systems. ..   http://www.johnsservice.net/