NuttyGambler,
I have a geothermal unit that discharges into my front .62 acre pond. Like someone said, only downside is the open area it could create in the ice. Other than that I see no disadvantages. However when it's really cold you can get pretty close to the discharge. If the open area bothers you you could probably weight the hose down and have it discharge into deeper water? My household well is a 20 gpm well pump.
I wouldn't expect it to add a significant amount of water if that is what you are after. I've watched mine and it kind of runs in the pond in spurts like turning on a big garden hose sparadically. It runs more often when it has to work harder as in summer and winter. I remember measuring the discharge and it was about 20 gpms.
