Be aware that there is an installation issue with Perian. As installed by the 1.0 PrefPane, both Perian.component and AC3MovieImport.component will be owned by a user that is unlikely to be on your system. The uid is set to 303307112, while the gid is 2456673755, which seem to be from a directory system (eg: Active Directory). The ownership is not necessarily an issue for the software's functionality, but it is certainly an oversight by the Perian guys, and was interfering with my ability to build a deployment kit for my users.

If you are having troubles with Perian, you should replace those permissions. Either use the Get Info panel to select a new user (and then copy the ownership to the contents), or use chown/chgrp from the Terminal. Disk Utility's permissions fixer does not correct this.