mcogilvie's correct; you don't organize during the weekly review; you do it as soon as a project comes up.

Also, in GTD, organizing does not mean brainstorming. In fact, in GTD there is very little brainstorming.

The purpose of the Organizing step is to accomplish the following:

1. Figure out if the project needs to be done now or later.
2. Putting the project in your Projects or Someday/Maybe lists.
3. If it's a current project, determining the Next Action.
4. Storing or trashing appropriate materials (putting an article you want to read in a tickler file, storing a brochure in a long-term file, etc.).

This shouldn't take an hour. Obviously, if you want to take time brainstorming about the project, you can, but you don't need to. All you need to worry about are the four things above.

(Unless I've missed something.)