Tim Powers has confirmed earlier rumors with the following news: "I can now say that Disney optioned On Stranger Tides and will use elements of the book in the fourth Pirates of the Caribbean movie. I can also say that I did not ever specify that Serena and I get parts in the movie or have dinner with Johnny Depp! (Not that we'd mind.)"Source.
The fit is an obvious one, as On Stranger Tides is about a pirate named Jack who goes in search of the Fountain of Youth. This fourth installment will be titled Pirates of the Caribbean: On Stranger Tides and will be released in the summer of 2011.
If you'd asked me what Tim Powers novel should be made into a movie, I would have picked Last Call or Declare, but this will certainly be interesting if much of On Stranger Tides actually makes it into the final movie.
Maybe this will finally result in Powers' publisher not letting his titles go out of print and get insanely expensive on the used market...