Pre-order benefits are often a nice way of getting folks to reserve games and boost pre-release figures for publishers to boast about. In the case of BioShock Infinite, 2K Games and Irrational are offering the "Industrial Revolution Pack," some DLC that lets players get off to a head start with in-game goodies.
What exactly do you get? The pre-order DLC offers up some in-game gear that will boost your combat prowess (unless you're just terrible at the game), 500 bonus in-game currency, five lock picks, and the Industrial Revolution puzzle game that unlocks stories of Columbia. Oh, and you can pledge your allegiance to either the Vox Populi or Founders through Facebook. Because, you know, gamers love Facebook?
Either way, there's a small trailer that promotes the pre-order bonus stuff. It doesn't sound like a whole lot to me, but if you were planning to pre-order Infinite anyway, getting something for your trouble is still great.
Industrial Revolution Pack - YouTube