A lot of people criticized iMovie 08 when it was first introduced. While you could say that iMovie 06 was a simplified version of Final Cut, iMovie 08 is more like iPhoto instead of Final Cut. Unlike iMovie 06 where you deal with projects individually, iMovie 08 scan your library for all movies and treat them like a library, like iPhoto.
I already can see several editing capabilities being limited in iMovie 08 compared to iMovie 06. However, 1 thing that iMovie 08 performed admirably, is Youtube uploading. On iMovie 06, I can create a great short movie, but then I have to encode it twice, once to export the movie from iMovie 06, second during uploading to Youtube. Encoding videos takes time, plus iMovie 06 doesn't have a quick preset for youtube. iMovie 08 makes this into 1 simple step, by simply clicking "Share," then "Youtube." iMovie 08 will automatically encode and upload the video in 1 go. I haven't done any video editing on iMovie 08 yet, but the quick upload to Youtube is greatly welcomed.
Apple is focusing more on quickly processing your movie and sharing it instead of a video editing app with iMovie 08. Obviously Apple wants you to buy Final Cut Express/pro if you need a real video editing app. Luckily, iMovie 06 is available for download now, free for iLife 08 users.