I missed the mini-series, so maybe I'm missing some old plot elements. However, I've noticed in the last two episodes that the main characters seem to fear that people they know have been replaced by cylons.
Perhaps there once was a real Boomer, but my impression from watching the series and hearing her orphan story is that there was not. Nor have I seen evidence that either of the other two cylons found on Galactica were ever real.
Has there ever been a case shown (yet) of someone human being replaced by a cylon, or have all humanoid cylons been simple sleeper agents with phoney backgrounds?
[Spoiler, if you've waited two weeks to see your Tivo/videotape]
On a seperate note, I'm a little confused by Baltar refusing to expose Boomer now that his test shows her to be cylon. I know why he didn't tell Boomer at the time, she'd have killed him. But he could have told Adama later in perfect safety, and proven himself an irreplacable hero of the fleet. (Whether he ever took the time and effort to run another real test or not.)
What's more, the decision to fake all the tests as "green" seems to be his idea; not the idea of the chip in his head, based upon their conversation at the end of this weeks episode. (Though she does seem to have dropped the threat that he build a working detector or else she will kill him. Not sure why she makes him build it, if she isn't going to make him use it.)
-S'Cipio