Last month I did a new ConfigMgr 2012 SP1 installation. For installing a specific application it was needed to do a Group Policy update first. Case is this isn't actually allowed during OS deployment. When doing a "GPupdate /force" during a task sequence the system will be hanging on that specific step, and stops deploying. Microsoft has the following to mention on this topic:
The Setup Windows and ConfigMgr task sequence action is responsible for running Group Policy on the newly installed computer. The time at which Group Policy is applied during the task sequence action depends on the operating system being deployed. For Windows XP and Windows Server 2003, Group Policy is applied after the Setup Windows and ConfigMgr task sequence action is completed. On Windows Vista and Windows Server 2008, Group Policy is applied after the task sequence is finished.
When using Windows 7 or Windows 8, Group Policy is applied after the task sequence is finished also. A workaround which can be used is to add a mandatory deployment for an application, which will be active after deployment. That way the application will be installed after deployment, when Group Policy is already active.
Just remember: adding an extra last step in a task sequence for a computer restart (or multiple restarts) doesn't resolve this issue. A computer restart is needed after the task sequence deployment to make Group Policy active on the system. Hope it helps!