So Ausiello gave us this:

Sam learns in the season finale that ******i** ****** is the ***** **** that has ** ** broken ****** ******* can ***e.

Which to me seems to say:

Sam learns in the season finale that murdering Lilith is the final seal that has to be broken before Lucifer can rise.

Which implies one of two things. Either Sam is actually trying to break the seals and free Lucifer by the season finale (unlikely), or he's still just trying to kill Lilith, but finds out that doing so would bring on the apocalypse, thus presenting a dilemma.

The question then becomes: Will he go through with it anyway?

I'd like to think yes. I've been jonsing for Sam to be evil since season two. It's about time. And it would fit with the earlier spoiler that the final episodes are all about Sam vs. Dean. Dean's been tasked with preventing the apocalypse, and now Sam wants to cause it.

Plus, that scenario would give us the ironic twist of Dean having to protect Lilith from Sam, which would be epic on so many levels. :D