The magic 8 ball says "Better not tell you now"
I consulted my magic 8 ball -- yes I have a magic 8 ball, and it is a geeky kind of cool -- and I have come to the conclusion that the amulet will be what saves Dean from going to hell. The demons, or at least some of the demons know about the amulet, and since they want Sam to go darkside without Dean, Ruby gets on Bobby's good side by fixing the colt, in an effort to gain information on the amulet from him(since he is the one who gave it to Sam in the first place. He is also the one who gave them magic charms last season as well. It seems to be his THING). I only worry that this will result in Bobby's torture and/or death, in which case Kripke might need to go into the witness protection program, because fandom will be MAD!
In any event, this might be too simple. We have always thought that the amulet would be some sort of protection symbol for Dean, and it has been theorized that it is connected to Joseph Campbell's Hero's Journey, or that the amulet actually represents the Mesopotamian Bull-man who helped people fight evil and chaos, and even Cernunnos whose depiction at times bears a striking resemblance to the amulet... but to have Dean's get out of jail free card be so simple... might be too easy.
__tiana__ thinks that I am SUPER EVIL because what I originally wanted to happen was for Dean to be sent to hell, for Sam to go after him like in the Orpheus and Eurydice tale, and have him doubt that Dean is with him right at the end and lose Dean forever. The last shot of the season would be Sam beating his fists on the closed Hell's Gate and screaming, and we would have to wait until next season for Sam to save Dean. Think of it. A whole summer of collective fandom PAIN!!! It would be AWESOME!!!
But then... it would all pay off next season as Sam uses the demons against the armies of Hell and gets Dean back. Sam would yell "Dean", Dean would yell "Sam" and then they would hug, and fandom would cry, and it would be BEAUTIFUL!
Of course, the fact that I have a vid idea that requires the ending of season 3 to unfold this way... has NOTHING TO DO WITH IT!!!