No, it is not a Battlestar Galactica spoiler if I tell you that there is an image of Starbuck and a bonfire in the "coming soon" scenes for the second part of "Revelations," the stunning episode that ended the first half of season 4 over a week ago. Though both parts of the episode were meant to be shown back-to-back, according to the writers, we're going to have to wait until 2009 to find out what happened to all those humans and cylons questing for Earth. But one thing we are pretty sure about — and that's the true meaning of Starbuck's bonfire. OK, now there will be spoilers ahead.
Galactica: Variants has a pretty awesome shot-by-shot analysis of the scenes from next episode. There is much discussion about whether the last cylon is on Earth, and might have used advanced, futuristic technologies to manufacture a Viper replica to send Starbuck back to the Galactica in. This scenario points to a highly advanced Earth civilization. But why exactly is she staring into that funeral pyre so intently? We already know, based on a shred of script that got passed around, that it's because she's found her old Viper — and her old body! And she's burning them.
So Starbuck definitely isn't a cylon. In fact, she's probably some kind of vat-grown person with Original Starbuck's memories downloaded into her brain. Which begs the question: If there is a technology that allows humans to be uploaded to a computer, then downloaded again into a new body, aren't humans essentially the same as the cylons? Ohhh, ponder that one, my astronauts!