The package contents have been moved to
compiz-plugins and the dummy package was removed in 12.10.
This was the state in 12.04:
$ aptitude show compiz-fusion-plugins-extra
Description: transitional dummy package.
This package ensures a clean upgrade path, and can be safely removed after the
$ aptitude show compiz-plugins-extra
Description: Collection of extra plugins from OpenCompositing for Compiz
The OpenCompositing Project brings 3D desktop visual effects that improve
usability of the X Window System and provide increased productivity.
This package contains extra plugins and themes contributed by the community
giving a rich desktop experience.
compiz-plugins-extra now is a dummy package in 12.10, too.