Via Edward Champion, we learn that Tom Tykwer (Run Lola Run) is trying to adapt David Mitchell's Cloud Atlas for the screen, with the help of the Wachowski brothers. Note that this article erroneously (I hope) assumes that Tykwer's adaptation will focus on only one of the novel's six narratives, and also that there's no indication of an actual production deal in place.
Champion calls Cloud Atlas 'an unfilmable novel', but I'm not sure I see how it is any more so than any other big, sprawling piece of fiction. The nested narrative structure is unusual, but there have been plenty of films--including Run Lola Run--whose narratives were far less linear. Unlike, say, Possession, Cloud Atlas makes the switch from story to story, period to period at only a few clearly marked locations--in that sense, the shape of the movie is predetermined, and 'all' that's left for a screenwriter is to fill in the details of each narrative. Which of course is the problem, but it means that Cloud Atlas is no more unfilmable than Pride and Prejudice, and for much the same reasons: because there's too much going on in the novel to cram into at most three hours. That sort of problem has been solved well on occasion, and badly much more often. I guess we'll have to wait and see.