Quite a lot is (inadvertently) revealed during the final seconds of this interview and some of it, in my opinion, opens up for possibilities for a Sam/Kurt (or at least Kurt/Not-Him) pairing.
http://www.afterelton.com/tv/2010/10/glee-blaine-kurt#comment-162130(Video interview)
Towards the end there, Darren says that he hopes he gets to come back, which indicates that his character will "go away" (and/or that he won't be featured much). They haven't filmed much yet, but Darren knows that his contract is only X or so episodes. He also says he hopes he'll come back, which indicates that plot-wise, his character isn't going to stick around for long and certainly not for a lot of screen time. If he and Chris are to become boyfriends, you'd think he wouldn't need to hope he'd get to come back because then it'd be a certainty he'll come back. Of course, this could just be Ryan Murphy keeping even Darren in the dark, but let's keep our fingers crossed, shall we?
All of this, in my opinion, means that he probably isn't Kurt's future boyfriend, which makes a lot of sense. Ryan Murphy wants Kurt and his new boyfriend to be the school's new power couple and prom King and King and for that you need someone at William McKinley High School. And he probably also has to be at least a recurring character and not simply a guest star (or special guest star).
So Blaine is probably just a temporary romance (Kurt's first kiss, his mentor, a friend). Things are looking up for the Kam (Kurt/Sam) shippers. Maybe Sam's secret is that he's bisexual and he'll end up dating Kurt in the end.
After all, even though Chris Colfer said there was no romantic chemistry between the two in the first four episodes, there was some in "Duets" when Kurt at least was almost-pursuing him. And since then, we've had several instances where Kurt's thrown Sam looks (like in the last episode, when Sam was discussing his abs) and even some where Sam's thrown Kurt some! And Sam looked quite intrigued when Kurt performance "Le Jazz Hot".
Also, remember, they have never stated that Sam and Kurt will never become boyfriends. They've merely said thing such as "There wasn't any romantic hints in the first four episodes" and "I haven't read anything like that in the scripts yet" (a few weeks back). With Idina, they outright said "No, she's not going to be Rachel's mother" and she still ended up being her mother! This time they're not even denying it outright!
So I'm calling it now: Sam will be Kurt's true love interest in the end.