Yep, they are currently working on adapting Irrational's biggest game yet to the big screen. It's apparently the second biggest video game to movie deal yet, and the number one such deal, Halo, ended up falling through anyway.
http://www.scifi.com/sfw/news/sfw_news_20080512.html
Cool. That's funny though, because I just saw the "City of Ember" trailer before Prince Caspian, and for some reason it really reminded me of Bioshock.
I heard someone say that they're actually going to start the movie with the discovery of the Adam slug, followed by the New Year's Riot.