My problem with once saved, always saved is that it puts forth a teaching that once someone accepts Christ, they can live their life as a child killer, rapist, drunkard, etc etc and never have to worry because they'll still go to heaven since they were 'saved' when they were young. I fully believe that someone can willingly walk away from God after salvation has occurred and that if they die before repenting they will spend eternity in hell by their own choice. God will never be the one to turn his back on us, but He certainly gave us the free will to turn our backs on Him.