Taken from Technet:

The following items are new or have changed for desired configuration management (now compliance settings) since Configuration Manager 2007:

• Configuration Manager 2007 desired configuration management is now called compliance settings in System Center 2012 Configuration Manager.
• Configuration Manager provides a new built-in security role named Compliance Settings Manager. Administrative users who are members of this role can manage and deploy configuration items and configuration baselines and view compliance results.
• An administrative user can create registry and file system settings by browsing to an existing file, folder, or registry setting on the local or a remote reference computer.
• It is now easier to create configuration baselines.
• You can reuse settings for multiple configuration items.
• You can remediate noncompliant settings for WMI, the registry, scripts, and all settings for the mobile devices that are enrolled by Configuration Manager.
• When you deploy a configuration baseline, you can specify a compliance threshold for the deployment. If the compliance is below the specified threshold after a specified date and time, System Center 2012 Configuration Manager generates an alert to notify the administrator.
• You can use the new monitoring features of System Center 2012 Configuration Manager to monitor compliance settings and to view the most common causes of noncompliance, errors, and the number of users and devices that are affected.
• You can deploy configuration baselines to users and devices.
• Configuration baseline deployments and evaluation support Configuration Manager maintenance windows.
• You can use compliance settings to manage the mobile devices that you enroll with Configuration Manager.
• Configuration item versioning lets you view and use previous versions of configuration items. You can restore or delete previous versions of configuration items and see the user names of administrative users who made changes.
• Configuration items can contain user and device settings. User settings are evaluated when the user is logged on. Examples of user settings include registry settings that are stored in HKEY CURRENT USER and user-based script settings that an administrative user configured.
• Improved reports contain rule details, remediation information, and troubleshooting information.
• You can now detect and report conflicting compliance rules.
• Unlike Configuration Manager 2007, System Center 2012 Configuration Manager does not support uninterpreted configuration items. An uninterpreted configuration item is a configuration item that is imported into compliance settings, but the Configuration Manager console cannot interpret it. Consequently you cannot view or edit the configuration item properties in the console. Before you import Configuration Packs or configuration baselines to System Center 2012 Configuration Manager, you must remove uninterpreted configuration items in Configuration Manager 2007.
• You can migrate configuration items and configuration baselines from Configuration Manager 2007 to System Center 2012 Configuration Manager. During migration, configuration data is automatically converted into the new format.
• Settings groups from Configuration Manager 2007 are no longer supported in System Center 2012 Configuration Manager.
• Regular expressions for settings are not supported in System Center 2012 Configuration Manager.
• Using wildcards for registry settings is not supported in System Center 2012 Configuration Manager. If you migrate configuration data from Configuration Manager 2007, you must remove wildcards from registry settings before you migrate otherwise the data will be invalid in the System Center 2012 Configuration Manager configuration item.
• The string operators Matches and Do not Match are not supported in System Center 2012 Configuration Manager.
• You can no longer create configuration items of the type General from the Configuration Manager console. You can now create only application configuration items and operating system configuration items. However, if you create a configuration item for a mobile device, this is created as a general configuration item.