Sources backing up the above spoilers:
Aaron Douglas and Tricia Helfer have both said that some of the Final Five are revealed in the season finale. Aaron knowing obviously makes sense if he's one of them.
This reviewer confirms
that the final three episodes are doing the rounds (he's refusing to watch them due to temp sound effects and unfinished CGI though).
The Patriot Resource (I know, they've been wrong before, but they've also been right before) have also picked up on exactly the same rumours
. However, they say that it's Roslin, not Adama, who makes the mistake that leads to Baltar's release. They also claim that there's a fifth
storyline, in which Cally becomes convinced there may be another Cylon on board and she confronts Athena about it, who agrees to help her find and expose them.
The Chicago Tribune has an article
which backs up some of the above.
Bear McCreary, the BSG composer, has noted
that in the last two episodes he's done something very different involving music which ties directly into the finale storyline.
There's also one photograph of Roslin in the
Opera House and another
of Baltar, Six and Hera there which at least hints that those spoilers may be accurate.[/spoiler]
They finished filming the BSG Season 3 finale in early December and finished editing it a few weeks back. With the series going through what can only be charitably be called a late-season rough patch, it is quite likely that the SFC would be sending out review copies of the final three episodes for people to spread the word how awesome they are and get them watching again.
If spoiler #2 is accurate (specifically the one character), it throws open the field for the final candidate. Everyone is eligible.
That's the point of doing it. Everyone will assume that:
Is the other member of the Final Five but that's not necessarily the case. However:
[spoiler]Tigh being a Cylon very obviously explains why Three apologises to the Final Five in Rapture
. It would be for ripping out his eye.[/spoiler]