I agree with Theo. Once saved, always saved. However, if a person is truly saved there will be evidence of that in their life. Not that we don't fall from Grace.. if we didn't we wouldn't need it. A person who is truly saved by Christ has the guidance of the Holy Spirit and won't be at peace until they repent from their sin. I can't see someone who claims to be saved stand up and really believe that their sin is OK just because they have Christ as their Savior. If they're saved there should be a small voice nudging them and creating conviction and guilt. It happens, but God doesn't leave this behavior unchecked for long. I'll admit that I've ignored my sin, but ignoring it doesn't make the conviction go away.. it usually leads to distancing from God and feeling really crappy about myself. After awhile you get to a place where love and joy escapes you and you either turn it around and repent, or remain miserable an open the door to more destruction.
Yep, can't have 50% of Jesus. I remember the day that I realized that Grace is not just a gift we receive to do whatever we want with. The other part of that equation is a willingness to give ourselves to Christ and allow him to work through us to reach others. This is what truly being saved means to me. He wilingly sacrificed for us and we willingly sacrifice our will so that others can see Him in us and accept Him too.