I agree with you on your entry about forgiveness. I believe the most vital question is, "do they DESERVE to be forgiven?" Have they tried to make amends in some way? Words are great, but has there been action to show they are willing to do better?
And even then, as you said, forgiveness is still within your power. But I honestly feel it is better to rid yourself of so much negativity. You should never feel as if you're "helping" them by forgiving their behavior; it should be for YOUR benefit!