This command wipes backups done during SP1 upgrade,these backups are needed only in order to revert SP1 upgrade so no need for keeping it.

dism /online /cleanup-image /spsuperseded
Results is

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.
 
C:\Windows\system32>dism /online /cleanup-image /spsuperseded
 
Deployment Image Servicing and Management tool
Version: 6.1.7600.16385
 
Image Version: 6.1.7600.16385
 
Removing backup files created during service pack installation.
[==========================100.0%==========================]
Service Pack Cleanup operation completed.
The operation completed successfully.
 
C:\Windows\system32>

see http://blogs.technet.com/b/joscon/archive/2011/02/15/how-to-reclaim-space-after-applying-service-pack-1.aspx for explanation