Thanks to Nate for his comment, here's a prolonged response. He asked how we as Christians should think of earthly revenge.
The obvious answer is that we should avoid it, but I think it's slightly more complex.
In the Mosaic Covenant, the law prevented escalating conflicts by capping it at "eye for eye," etc, and that was extended by Christ with the blanket "turn the other cheek," which we all know. But the context of turning the other cheek assumes that the cheek is yours, and when it isn't, things do get a lot more messy really quickly: look at the Amish school shootings, or the "Deny Christ or I'll kill your son" scenario.
My personal standard on evil is that not all evil is an evil: there are many hard providences given to us by God, and we are to be stewards of them as much as of the blessings. (Which is why I hate Thomas Kinkade paintings with a passion. There is no conflict, no dragon to fight, and as such they are lies of a utopian world, and are a symptom of a generation of weak and cowardly Christians that fear pain rather than God and pine for the nursery while God calls for men to run with horses and love not their lives even unto death: look at His response to Job: "I make the young eagles lap up blood; I clothe the horse's neck with thunder...")
I would hold with Augustine's Just War theory so far as it goes--we don't fight the unarmed and the non-combatants, and we only fight to defend that which is ours and is being attacked--but when the attack has taken place and is out of our reach, I think that we are fully justified in exacting a punishment that meets the crime when the crime is against someone that is in our charge, though I don't think that we generally should.
The ideal situation is that we would have a just magistrate that wields the sword, and as a general rule, we should submit to the magistrate even when he is not just (such as our entire system), but I think that specific exceptions could arguably be made. The ones that come to my mind--the exceptions that I would be willing to make--are for rape and child abuse: were those committed against someone in my charge--against my wife or child--I think that I would be willing to kill the perpetrator, and I would consider it an execution. But for that I have no Scriptural leg to stand on, beyond the chasm between the actual law and our pathetic imitation of it.
This of course breezes by all of the possible factors: how much time has elapsed, who it was that committed the crime, was it an ongoing pattern, what was the nature of the crime, and on and on.
I guess that the bottom line for me could be summed up as follows: I would be willing to enforce God's law when it comes under my authority and when it is a hill that I'm willing to die on, so to speak.