The news that Arnold Schwarzenegger is back on I Am Legend is a little misleading because he's not starring, no that role is still penned for Will Smith, he will be producing the film however.

From Moviehole through a few other sources:

The latest incarnation of the film will be helmed by Francis Lawrence (“Constantine”) and star Will Smith.

"Entertainment Weekly claims that Arnold and Ridley Scott [originally] left the production because of a sky-rocketing budget said to be north of 108 million, but Arnold kept the producer title", says the site.

The film is based on the 1954 science fiction novel by Richard Matheson, about the last man alive in Los Angeles. He actually lives in a suburb of what was then a not-so-built-up metropolis.

It's an interesting tale, and if you think about the movie and switch back and forth between the possible leads - Arnie against Smith - it's interesting how the idea of the film changes in your mind. Which would you have preferred?