Might as well throw my hat into the fires of debate...

(I'll be using 'Ki' because it just looks cooler. Would Mortal Kombat
been as cool with a 'C'? I don't think so.)

>From what I've seen in movies, tv and fanfics, there seems to be two
ways of harnessing ki:
One way is to get it from yourself. This is the technique used by Ranma
and Ryoga's ego and depression blasts. Since it's you're using your life
force as a weapon, this drains you considerably unless you've been
training for a while. This can restrict the amount of ki blasts you can
do. It's harder to heal yourself using this method because of the power
source. If you're already weak and try to heal yourself, you'd be doing
more harm than good.
Another way is to get it from living things around you. This is kinda
like the Force from Star Wars. Depending on the amount of power you're
gathering, this method would not be a good choice if you're gathering ki
around people recovering from an injury of some sort. The plus side is
that it's less draining than getting the energy from yourself, meaning
you could pump out ki blasts like a machine gun. This method is much
better at healing because you're taking energy from things around you.
In anime, when you see someone charge up a blast, sometimes you see
little streaks (usually white) coming quickly toward the ki ball. That
is good evidence that the person is using energies from his
surroundings.

-Mark