What happened to Sam?

I think he came back and he's been hunting for a year (season 6 starts a year after 5 ended) by himself in order to let Dean "rock the white picket fence." But then something comes after Dean so Sam hunts it and then Dean gets all pissy cuz Sam has been back for a year and hasn't told him.
But I might be wrong.

I hate to bust some Sam bubbles but after rewatching the last season on dvd I still think he is Lucifer. but they might just be trying to make it look that way so people will watch & c if he is or not. you know a suspence kind of thing

After watching the preview, I honestly think it's Sam. But when I first saw the end to Swan Song, I thought it was Lucifer because of the way his face looked. Sort of angry, or full of hate.

I think Sam is alive and has been hunting the last year but has changed. There are things that make him different because he escaped hell and no one knows how?

All I'm sure about is that he can't be the same after hell. About the rest... I have no idea :(

I think its sam its gotta be sweet sam,but yeah the trip to hell would change a person,but still think its sam and not lucifer!!!!!