Q: Does Malfoy owe Harry a debt?
JKR: That's a great question and a lot of people wanted to know that. When Dumbledore said to Harry, Voldemort won't want a close associate who is in your debt, I wasn't implying by that there was any kind of magical bond there. It was more that Dumbldore's extensive wisdom and knowledge of human nature, he knew as Harry later thinks in book seven, he knew that Pettigrew would react a certain way to having saved his life. ... He's weak, fundamentally weak. Pettigrew is a very weak character. He's not someone I like at all. He's a weak person and he likes to gravitate to people who are stronger. Dumbledore is right. Pettigrew had an impulsive mercy... would Malfoy e [sic] in Harry's debt? I think the very worst burden Harry could have put Malfoy under was this one, that Malfoy has to feel any kind of gratitude. So I tried to show that slightly in the epilogue when they look slightly at each other and there's a, "Hi. It's so embarrassing, you saved my life. No one will ever let me forget it." I think, does he owe him a debt, probably not. I think Malfoy would go back to being an improved version of what he was but we shouldn't expect him to be a really great guy any time soon.
JK Rowling at Carnegie Hall 10.20.07
Personally, I would think Draco does owe Harry a life debt. Harry risked his own life in order to save Draco, who moments before would have happily seen Harry dead by Fiendfyre. I find it a bit of a discrepancy that Peter Pettigrew would have a life debt to Harry, but Draco Malfoy would not. That said, the "Hi. It's so embarrassing you saved my life" bit is absolutely hilarious to me :D