We're asked all the time about the size of the WinSXS directory. So much so that my original blog on the subject (located here: http://blogs.technet.com/b/askcore/archive/2008/09/17/what-is-the-winsxs-directory-in-windows-2008-and-windows-vista-and-why-is-it-so-large.aspx) is one of the top hit blogs on my teams site.
A question that comes up a lot about this particular blog is where the VSP1CLN utility is located on Windows 2008 installations. The VSP1CLN utility is used to mark the Service Pack 1 binaries permanent, thus reclaiming some of the disk space on those installations. I did a poor job of making that clear on the original blog, so I figured I would make it clear here. VSP1CLN is only available for machines that were RTM+SP1 installations. So, this means that the utility is only applicable to client installations. Why? Because when we shipped Windows 2008 Server, it already included the SP1 binaries and they were already marked permanent when it was shipped. This means that you not only dont need to run this on 2008 installations, but you cant.
If you install Service Pack 2 for Windows 2008, you can mark it permanent and reclaim disk space using the COMPCLN utility.