I'm building amateur radio equipment for 47 and 78 GHz. Maybe I will make it to 120 GHz eventually. Power is REALLY expensive up there, and I don't expect to get more than a handful of microwatts out of my equipment. That should be good for a few miles, though.
People I know who have made gear for 300 GHz and above say it isn't a lot different than using a modulated flashlight or laser. A 1 foot diameter parabolic reflector has a lot of gain.