Multiple problems here:
If I select all the files in the book, and export book to PDF, I get all the PDF presets, and lots of options. However, it always prints single page, and none of the videos work.
If I do not select any files, and export book to PDF, I get a smaller page with less options. With this, I get double pages, and the videos do work. So far so good. But if I select 'single page', it still gives me double page (as per the book layout).
There are two types of PDF, Print or Interactive, selectable from the dropdown in the export dialog. Sounds like you selected Print the first time and interactive the second. By default Interactive PDF exports spreads, and in CS5/5.5 the only way to swithc to single pages is to run a script. This has been discussed quite a bit elsewhere in the forum.