There are always requests here at Microsoft for reducing the footprint that the component store takes up (\Windows\winsxs). Applying a service pack to Windows Vista or Windows 2008 will increase the size of the store even more to allow for the staging of the binaries that make up the service pack itself. Because space considerations are very common in the server world, and sometimes in the personal and professional space, I wanted to make sure everyone knew how to reclaim space within the component store after applying a service pack.
For Service Pack 1 installations on Windows Vista, the tool to use is VSP1CLN.exe.
For Service Pack 2 installations on Windows Vista and Windows 2008, the tool to use is COMPCLN.exe.
Running either tool will remove the ability to uninstall the service pack, so make sure that you are happy with your Windows installation before doing this. The amount of space reclaimed should be roughly the equivalent of the files that comprise the service pack. Both tools can be run against an online (running OS) or offline image (image mounted in IMAGEX or another tool).
NOTE: You cannot run VSP1CLN on a Windows 2008 installation because it is already on SP1.