Self Defense? Was George Zimmerman justified in shooting Trayvon Martin?

Let's assume that each of us has the right to self defense, and consider for a moment the circumstances that might reasonably force us to use that right.  It seems reasonable to me that I might use lethal force to defend myself at the point that an assailant demonstrated the intent to use lethal force against me.  I can't imagine much argument against that, but there are still some soft spots in there that are open to some interpretation.

• How can I determine my assailant's intent?  At what point does his action demonstrate lethal intent?
• Can lethal force be justified for anything short of lethal intent?  If my assailant only intends to cripple me, must I limit myself to crippling force in defending myself?

Let's consider a few hypotheticals.  Assume in each case that I am exercising legal concealed carry:

• A man attacks me with a knife.  I draw my pistol.  He continues to approach me still brandishing his knife.  Must I allow him to stab me to prove intent?  Maybe he just wants to cut me but not kill me.  Should I wait till he makes a lunge at my vitals or fire before he gets within arms reach?
• A man threatens me with a gun.  I take cover and draw my pistol.  He takes aim and continues to approach, circling toward my exposed side.  Do I fire before he clears my cover, wait till he finishes circling to allow a fair fight, or give him the first shot?  Maybe he'll just try to shoot the gun from my hand.
• A man sucker punches me, front mounts me, strikes several blows to my face and starts to pound my head against the sidewalk.  I draw my pistol.  He continues to strike blows to my head.  Do I allow him to keep striking me assuming that he wants to teach me a lesson but will stop short of killing me?

There's a word for people that give their assailant the first shot, and that word is deceased.  If I draw and you keep coming, there will be no second warning.  My obligation is to go home to my wife and kids, not to give you the benefit of the doubt.

Unarmed? Trayvon Martin was not an unarmed man

There was a boy in my community who was murdered a few years back.  I knew him, but didn't know him very well.  He was a nice kid who ended up where he shouldn't have been, and it cost him his life.  The murder weapon was a concrete block.  It was used to smash his head in.  Blunt force trauma, they would say if it was a cop show on TV.
The murder weapon was a concrete block.  It bears repeating.  When he was down on the ground, and his attacker raised that block up and brought it down on his head, is there a single one among us who would consider his attacker unarmed?  Of course he was armed.
Is there a fundamental difference between slamming a concrete slab onto a man's head and slamming his head into a concrete slab?  I would argue that there is not.  You could make counter arguments about the velocity at contact or the shape of the surface, but in the end it is still blunt force trauma to the head.
So at what point does a sidewalk become a weapon?

• Man walking on the sidewalk - Unarmed.
• Man standing on the sidewalk delivering a blow with his fist - Unarmed.
• Man in a front mount driving another man's head into the sidewalk - Armed.

I would go a step further.  He becomes armed the moment he makes the decision to use the concrete as a striking surface.  It becomes a weapon as soon as your assailant considers it a weapon.

Profiling? Exactly what you would expect from the neighborhood watch

Why isn't it universally recognized that the whole point of the neighborhood watch is to, um, watch the neighborhood?  It should be obvious that people you don't recognize bear watching more than those that you do, and that concealing your identity only attracts attention.  Surreptitious behavior stands out like a sore thumb.  

You can make the argument that there is no legitimate place for untrained civilians taking part in neighborhood policing, but once you accept a neighborhood watch as legitimate you must necessarily accept that it will watch the neighborhood.  Criticizing the neighborhood watch captain for profiling is ridiculous.  Profiling is practically his job description.  The function of neighborhood watch is to put eyes on suspicious behavior, and to let people know that there are eyes on them.
If you don't like being profiled, here's a tip.  Behave openly.  Identify yourself.  Be friendly.  Say hello.  Have a conversation.  Show your face.  That's the way that neighbors act toward each other.  Once you establish yourself as a neighbor there will be no need to watch you.