I'm going through the residential HVAC program at the local community college, mostly because it's interesting. I've always tinkered with furnaces in my house, and I installed a heat pump in my girlfriend's house earlier this year. My educational background is a couple years of Physics, and my "real" schooling right now is in human centered design & engineering (four year program). It would be neat if I could do something that involves HVAC and my formal training, but maybe it will continue to just be a fun thing. Seems like there is a lot of room for improvement in this trade.
I took my EPA exam a few months ago, and picked up a bunch of tools, so I've been using friends and family as guinea pigs. They are ready and willing since I already have a good reputation for fixing their cars and solving all their other mechanical problems.