SPOILER WARNING FOR BIOSHOCK (for all you PS3 owners)
First I've heard of the rumours... I think after the Good Ending (which incidentally made me cry, one of the few games to do so) the general feel was that this was supposed to be one of the grown-up Little Sister's, or a child of one, after they were rescued.
On that note, if it's a prequel, how could she know the model of the Big Daddy?
I'm loving the period music though, gave me memories of playing through certain levels.
In any case, this was one of the few games I purchased at full price (got the Collector's Edition too) instead of waiting for the price to go down, since it was worth getting for the experience. I hope that the plot will be as involving as the original, since the world was so absorbing with all those audio tapes etc.
Let's hope it won't be another 4 years before it's released...