Droopy:
I'm class D certified in Canada. Means I can legally transport a human external load. And that's one of a few prerequisites that have to be in place to conduct such operation. The training isn't hard, since most pilots who do that kind of stuff are usually quite proficient in longline operations already.
Knowing the legal side is just as important!
The helicopter itself has to be equipped with either a double hook system or a belly band in addition to the regular belly hook. Under no circumstances will such a load be flown on just one hook. There is also an airspeed restriction, which is 60 Kts with a load on the hook.
We use this kind of rescue as a last resort only on seismic or logging jobs or in the mountains during heliskiing operations.
Sometimes terrain, trees or the type of injury ask for this kind of retrieval though.
The load will be flown to the nearest point where emergency personnel is able to take over the injured person and not further. Usually it's just a short flight that sometimes doesn't even last 2 minutes.
Cheers!