Same problem here.
We have deployed Acrobat XI to 300 computers, and turns out that it pops up trial registration on each computer and user. The deployment package has been made with the Adobe Customization Tool and deployed with SCCM2007 to workstations. After hours of frustration we managed to get the software activated by creating a provisioning XML with APTEE and updating the version to 11.0.01. Still the sofware pops up the trial registration window.
By doing the previous we even managed to get the "Product Registration..." to show up in the Help-menu. Clicking it opens a web browser and redirects to this helpful page: http://www.adobe.com/special/errorpages/404.html.
Tomorrow we're going to rollback to X, since currently Acrobat XI is unusable.
Similar problem with single user installation: http://forums.adobe.com/thread/1119785