Microsoft has introduced Snapshot Backups for Active Directory in Windows Server Longhorn Server. This feature uses the VSS API as many other Microsoft products and technologies use for the same purpose.
The snapshots can be generated/taken at anytime and can also be scheduled.
Active Directory Administrators can then mount a snapshot from a given time and browse Active Directory with the exactly same content at the given time, and perform restore individual objects. I cover Active Directory Snapshots in my 2 day course "Active Directory features in Longhorn Server" among many other new features. You can read more In detail about my lab here: http://www.truesec.com/PublicStore/product/Active-Directory-features-in-Longhorn-Server,433,147.aspx

Here is a step-by-step guide for anyone that wants to get started with Active Directory Snapshot Backups by their own now since Longhorn Server Beta 3 is released public to the web.

1. Create and mount an Active Directory snapshoot backup
   1. Type the following command at a domain controller running Longhorn Server Beta 3:
      ntdsutil and press enter. Type act inst ntds and press enter.
   2. Type snapshot and press enter, type help and review the options.
   3. To create a snapshot type the following command:
      Create and press enter, Verify that the command completed successfully.
      Note: This command can be scheduled using an at job.
   4. To mount the snapshot type the following command:
      mount <snapshot guid> and press enter.
      Note: The snapshot guid is reported by the create command output.
   5. Verify that the snapshot was successfully mounted.
      Note: Write down or memorize the path to the D:\ partition (since the database resides within that partition.
      Sample: C:\$SNAP_<TimeStamp>_VOLUMED$\
   6. Start Windows Explorer and navigate to C:\ and ensure that you can see the there mount points, and browse them.
   7. Start a new command prompt by click start click run and type cmd and press enter.
   8. Type the following to start the offline browser as a live directory services.
      dsmain –dbpath:C\$SNAP_<TimeStamp>_VOLUMED$\NTDS\ntds.dit –ldapport 345 –sslport:346 –gcport:347 –gcsslport:348 and press enter
   9. Verify that the start-up was complete.
2. Browse a snapshot backup using LDP.exe
   1. Start a LDP.exe by click start and click run and type ldp.exe and press enter.
   2. Within ldp.exe click the Connection menu and choose Connect and specify the following options:
      Server: localhost
      Port: 345
      Click the OK button.
   3. Click the Connections menu and chose Bind (or press Ctrl + B) and accept the default settings (bind as currently logged on user) and click the OK button.
   4. Click the View menu and chose Tree (or press Ctrl + T), Choose the Domain NC and click the OK button, and verify that you can browse the Domain NC from the snapshot backup.
   5. Close ldp.exe
   6. In the command prompt where you launched the DS Offline Browser (dsamian.exe) and press Ctrl + C to kill the instance, Type exit to close the command prompt.
   7. In the command prompt where you running ntdsutil with the snapshot context, type the following command:
      list mounted and press enter.
3. Dismount and delete an Active Directory Snapshot backup
   1. Type the following command to dismount the snapshot backup:
      Dismount <snapshot GUID reported by the list command above> and press enter.
   2. Type the following command to delete a snapshot backup
      delete <snapshot GUID reported by the list command above> and press enter.