I have - the cost of installing such a system makes it questionable if it will ever be worth it. I've seen a few places that have it and they work great year round and are cheap to operate. However the payoff from the install if 50+ years despite the cheap costs. Everyone hopes the install lasts that long, but a lot can go wrong in 50 years. (the equipment probably won't last 50 years, but that will be cheap enough to replaces, it is the pipes in the ground that better last 50 years)
A large chunk of cost is drilling the holes for the loop. New, compact drilling rigs that use 10' drill sections are a good deal cheaper to run labor-wise and require less space to maneuver. Costs will come down as more companies switch to these rigs.
