WHAT IS AN EMPATHY CHECK?
    The basic principle behind an empathy check is: does the character feel sorry, regretful, or guilty about what he just did, or what he has done recently.  It is kind of like a conscience.  A friend of mine (Ghostlord) reminded me of how much this is like a sanity role in CALL OF CTHULU.  I had completely forgotten about that game until he reminded me.  The basic roll is against the current EMP score.  If the roll is less than the current score, the character feels a bit regretful, sorry, heelish, or guilty, or whatever about the cause of the empathy check.

WHEN SHOULD I DO AN EMPATHY CHECK?
    Ah, the age old question.  When should this be used?  When do you think this should be used?  I personally think that this is a matter of common sense, and GM discretion.  You could do it for every combat encounter, if you feel it justified, but I don't so I wouldn't.  I use this whenever my players do some kind of random killing.  If my player just goes out and shoots some bum for no reason, that would be worthy of an empathy check.  Random drive-by-shootings, pedestrian hunting, even playing potentially deadly practical jokes.
    Now, here is another condition I have used this for in the past.  Shooting someone who is already dead.  Now this can be tricky, because there is always the guy who will walk up to someone they just killed, and pump one or two more 10 mm rounds into his chest to "just make sure" he is dead.  This I have nothing against, if it is done properly, appropriately, and at the correct time.  If you have been trying to take down some metal head for 20 or 30 rounds of combat, then all of a sudden he just collapses, I would have nothing against pumping him with a few pistol rounds(maybe one or two) or another shotgun round.  But I am against, in the same situation, strapping dynamite to the guy and blowing him in 50 different directions.  That is just uncalled for.  I've unfortunately had players who've ripped up entire streets, trying to kill a guy, using C6, grenades, rockets, fully automatic rifles, sniper gear, and some other things which I don't immediately recall.  I made him take a huge empathy check for all the damage he did when he finally took the full-body-conversion down.  And unfortunately he passed.  He passed against all the damage to the streets, against the guy, against himself, and against the 20-some-odd civilians he killed or severely injured. (I think he had an empathy of like 3 or 4 at the time).
    As you can see, empathy checks applies to more than just people.  It applies to situations, animals, organisms, etc.

SOLO'S AND EMPATHY CHECKS
    Now I know some of you are thinking, hey, I'm a solo.  I am a professional killer, I don't have to worry about this.  WRONG!!  I have learned something this year, talking to many soldiers.  More than not, most are what they call "Doves" instead of "Hawks".  Doves are peace lovers, and Hawks are war lovers.  Not only that, from what I've also learned, talking to some Vietnam veterans, many regret and have deep emotional scars concerning what they saw and did.  Many regret being ordered to shoot vietnamese children, and women (generally considered civilians and noncombatants).  I don't blame them either, but getting back to the point: Solos (for the most part) are exsoldiers.  Granted they have been hardened by the violence that they witnessed in the army, and on the street (for those of us who came up on the road of bad breaks and playgrounds of hard knocks.  Example, when my character was forced to shoot his girlfriend in order to get her back (see Trax's bluebook), I forced an empathy check on myself (I consider those of us who do these kinds of things to ourselves are really pushing the role-playing envelope).  My guy passed (but barely), so he did it, but he really did everything he could to make sure he was able to have her revived.  Even as Trax was pulling the trigger, his doubts grew.  And when he watched her die, they peaked (it was one of the first, and last since, I let Trax actually shed a tear - amazing considering he had no tear ducts).  So, by this hardening, I think it is appropriate to give the Solo a bonus.  The bonus should be decided by the GM.  It should be anywhere from a +1 to a +3, anymore and balance will be lost.

OTHER CHARACTERS AND EMPATHY CHECKS
    Other characters, of a nonsolo type should not recieve this bonus.  Solo Types include but are not restricted to: ACPA pilots, soldiers(any branch), Nomads(Nomads should be restricted to a +1 and +2 left for the REALLY hardened), Covert Ops, anything with EXTREMELY STRONG combat relations.
    Now other characters are gonna be tricky.  Everyone is on a different level of expossure to violence.  A fixer has seen more violence (and probably been the cause of half of it) than say a super model; therefore, a fixer is more likely not have as much of a problem seeing the scene than a super model would.  Also, he probably wouldn't be as shaken as the model would.  I run other roles as follows: if the character is very stret based, and gets out often, and has been seeing heafty violence all, or a good deal of his or her life, then no adjustments to the role should be made.  If they are tower dwellers(as I call the upper class), and don't get down to the street much, and consequentially don't see as muchb blood being spilt, will have to make more frequent, and penalized empathy checks.  When dealing with this type of characte, I would also recommend a COOL roll, have failure result in queezyness, screaming in horror or terror, or even shock(if the scene is disturbing enough).

THIS IS ALL FINE AND GOOD, BUT WHAT ABOUT THOSE WITH NATURALLY LOW EMP SCORES WHO RUN AROUND DOING THIS KIND OF THING?
    Well, if that is the way their character is, then you can't blame them for staying true to their character.  However, murder is still not greatly tolerated by the local police forces, and a string of murders are especially going to catch the Police's eye.  Also, who is going to hire a 'runner who enjoys murdering people?  The only person who wouldn't mind is someone who is insane, or so bent on vengence that he would throw his kids and/or grandkids into harms way.  Think about these kinds of things when you next see your players becoming berserkers.

LITTLE THING I NOTICED IN NEVER FADE AWAY AND CONCLUSION
    In the end of the story, NEVER FADE AWAY, Johnny Silverhand pulls out his pistol, and simply, and purposefully blows the Arasaka Corp's brains across the far wall.  Now, you might be thinking I'm going to say, HEY!  JOHNNY SHOULD HAVE HAD TO MAKE A ROLL FOR THAT!  But you know what?  It would have killed the drama worse than the "death" of Alt Cunningham.  This is a situation where a roll would not have fit in too well.  The point I am making, is that, if you want to use the empathy checks, more power to you, BUT don't over do it, and don't let your players get too carried away.