The update provides enhanced performance and stability. Version 2.0.1 also supports the iMove 2 Plug-in pack, which Apple has also released for electronic download.
The plug-in pack contains 11 additional effects, transitions and title templates. You need to install the 2.0.1 updater to use them. Apple will release iMovie 2 for electronic download in September, but has no plans to release a CD version, as it claims the take up of the original iMovie on CD was insignificant.