2K’s put up a lengthy Q&A with some of the chaps working on the PS3 version of BioShock on the mysterious survivor mode, as you can see here.
In a nutshell:
What exactly is survivor mode?
It’s a new, highly challenging difficulty mode exclusive to the PlayStation 3 version of BioShock.
How does this differ from Hard Mode?
You’re more vulnerable, enemies are tougher, every resource is more precious.
Loads more through the link.