my parents put geothermal into a lake here in central ontario, and they have been very happy with it. yes, there are problems with icing up on the pipes, but they wired the pipes to a bunch of steel reinforcing mesh and concrete blocks to keep it all down...
As I understood the installation, it was a matter of how long the pipe is in the lake.
One of the best things for my folks is the summertime air conditioning the system provides.... ontario can get quite hot and humid in the summer and fall.
