My daughter is now 18 and I always had a hard time forgiving her if she lied to me. I feel that trust is one of the most important aspects of a relationship, including the relationship with your children.
I had found alcoholic beverages in her room when she was 16 and she denied that they belonged to her. This was unbearable for me. So we had a talk. I spoke of the dangers of drinking and the fact that it is illegal to drink until she was 21. I know that many teenagers dabble with alcohol so I could handle that my daughter did, too, as long as she was honest about it and it didn't become a problem.
Since that time I can only remember one occassion when she called me to pick her up from a party. As it turns out she wasn't the one consuming alcohol but the friend who was supposed to drive her home did. I picked her up and we found out that her friend totaled his car. He was not hurt. Her honesty on that night made up for the lie in the past.
I am unaware of her lying to me since. She has come to me with many tough questions and shared her problems and secrets with me. I know I have instilled the value of honesty and it is heart warming to know she has heeded my advice.