When Apple released iMovie '08 in August of 2007, many users were upset by the decision to move the timeline from the bottom of the app's window to the upper left-hand corner. The outcry was so loud that Apple made iMovie '06 available for download.
Now, version '11 lets you put a vertical timeline back in place. As TidBITS explains, it's a simple as swapping the Events and Projects browsers. Yes, you can make that swap in iMovie '08 and '09, but this is the first time it will result in a horizontal timeline.