As I've written before, I don't think Harry's scar is a horcrux. Basis? I think horcrux creation involves some kind of spell, and when Voldemort zapped Harry and his family, he didn't perform any spell; however, I don't remember where I read that or if I read it at all. I'll have to re-read the portions of Book 6 that discuss horcruxes.

Travis over at Sword of Gryffindor has an interesting theory. In his quest for horcrux clues, he references a passage in Book 1, Harry Potter and the Sorcerer's Stone.

Travis takes us all the way back to Harry's first night at Hogwarts. He'd just finished eating a generous meal after having been sorted into Gryffindor House. Just after the sorting, Harry makes eye contact with the Potions Master, Professor Severus Snape, whose ominous presence even this early in the game portends shadowy, creepy, and mysterious things. When Harry's scar begins to hurt, he thinks it has to do with Snape. Professor Quirrell, sitting beside Snape, is the reason. More precisely, Lord Voldemort is the reason.

Let's look at the passage:

Perhaps Harry had eaten a bit too much, because he had a very strange dream. He was wearing Professor Quirrell’s turban, which kept talking to him, telling him he must transfer to Slytherin at once, because it was his destiny. Harry told the turban he didn’t want to be in Slytherin; it got heavier; he tried to pull it off but it tightened painfully - and there was Malfoy, laughing at him as he struggled with it - then Malfoy turned into the hook-nosed teacher, Snape, whose laugh became high and cold - there was a burst of green light and Harry woke, sweating and shaking. (Harry Potter and the Sorcerer’s Stone, Scholastic, 130)

At this point, no one knows that Voldemort is inside the turban. Travis surmises that this dream is very significant. He believes it may be a clue that the scar on Harry's forehead is a horcrux.

We know that Voldemort has possessed Quirrell and is hiding inside his smelly turban, waiting for a chance to steal the sorcerer's stone so he can gain immortality. Why would Harry just happen to dream the turban is talking to him, when near the end of the book, the turban actually does "talk" to him? Coincidence? No such thing.

We know there's a connection between Harry and Voldemort, so I believe Harry was reading V's thoughts the way he's been able to throughout the series.

Travis and I agree on the connection between the two, but here is where we diverge. I don't believe the connection necessarily means the scar is a horcrux. The dream was foreshadowing Voldemort's plans as well as the fact that he used the Avada Kedavra curse on Harry and his parents. We learned for the first time in Book 4, Harry Potter and the Goblet of Fire (correct me if I'm wrong), that Voldemort used this killing curse, which explains why Harry had faint memories of seeing green light as a baby and why he sees the same light in this dream.

In Book 5, Harry Potter and the Order of the Phoenix, we learn that Voldemort is an accomplished Legilimens (mind reader) and that Harry "inherited" this trait from him. He was able to read Voldemort's thoughts then, and he's doing the same in this dream.

Travis says the dream is a clue that the scar is a horcrux, and the horcrux is the reason the two have a connection. I say the dream is only foreshadowing the ending of Book 1 and Harry's ability to practice legilimency, as revealed in a future book.

That was fun.