Obviously, this presents a challenge in writing the screenplay -- not only must the screenwriter deal with a jagged time-line, but it also has to come off as smooth and realistic, not jumbled and experimental. The novel is also 518 pages long, which means a lot of cutting in the story. Since the tale isn't linear, cutting any piece means re-jigging the past, present, and future of Henry and Clare. It is, therefore, not surprising that news has come of some script re-writes for the upcoming film.
The original screenplay was written by The Notebook scribe Jeremy Leven, and will now be re-written by Bruce Joel Rubin -- the man responsible for both Ghost and Deep Impact. He's got both romance and strange science under his belt, so this might bode well for the adaptation, which has been in development since 2003, before the novel was even released.