Akma has been discussing the theory and practice of forgiveness in great and clarifying detail.
One of the interesting insights in Nonzero is the great survival value of forgiveness. In order to gain non-zero sum benefits, trust and communication are necessary, but how one acts towards betrayal is very important. Avoiding the cycle of revenge and mistrust that lead to war and other negative sum outcomes is important. Nonzero's discussion of iterated prisoners dilemmas, based on Axelrod's work is interesting, in that it explains the advantages of the 'Tit for Tat' strategy, but more recent research shows that more forgiving strategies win out in the long run, especially over generations.
The Templeton foundation has gathered a lot of research into forgiveness here. Much food for further thought:
For example, This experiment concludes:
...this study suggests that inadvertent transgressions can be overcome through overlooking some of the offenses of one's partner (which might have been prompted by one's own hurtful behavior), and also, by refraining from allowing one's own inadvertently hurtful behavior from starting a precedent for mutual hurt in the relationship. Thus, willingness to forgive the inadvertent transgressions of one's relationship partner, but especially contrition for one's own hurtful behavior, appear to be critical ingredients for long-term success in interpersonal relations.