I don't know, but from MacWorld's description of iMovie '08, it sounds like a real step backwards. Posting to YouTube is a natural and helpful feature that's sorely lacking for any Mac users under the age of about 33, but why the heck would Apple gut so much of the rest of it? From MacWorld's "First Look":

Unfortunately, iMovie ’08 also offers no support for third-party plug-ins, choking off (for now anyway) a healthy niche business that has provided effects and transitions not found in iMovie itself.

Forget about the convenience of setting bookmarks to locate sections of your movie while editing.

Gone, too, are DVD chapter markers—Apple clearly believes that the future of distribution is online or via mobile devices, because the link between iMovie and iDVD is now tenuous at best. You’ll have to export your movie [from iMovie '08] to QuickTime, open it in iMovie HD 6, and add markers there before pushing it out to iDVD if you want to retain the capability to have multiple chapters on a DVD.
[emph mine]

Wow. And all this comes with a sys req of a G5 or an Intel Mac, as I've lamented previously. It's no wonder Apple's offering to replace the new version of iMovie with the old, free of charge. Kinda like Apple's support of 3D gaming, things sure seem rushed around here.

(Here's a nickel that iLife 08's release delay came from waiting on iMovie '08 to make it out of testing, and that things would have taken even longer if they hadn't started slashing features. Seems like I've blogged on that easy way out (and my taking it) before as well...)