Nice surprise for a Friday. According to this post on the 2K forums, all "activation limits" have been lifted from the PC version of BioShock.
"Good news! As promised, all activation restrictions, including install limits, have been removed from BioShock PC as of today," said community manager Elizabeth Toby. "You don’t have to patch or install anything for this to go into effect for your copy of BioShock – it’s already done!"
BioShock boss Ken Levine had said previously that DRM would be removed from the game when retail sales were "no longer a factor."
So there we are.