I wanted to bring everyone's attention to a recent blog I worked with on a co-worker of mine regarding issues we've seen with locking down permissions on componentized directories.  It's a good read and an easy plug for my team site.  Enjoy.

http://blogs.technet.com/b/askcore/archive/2011/12/14/troubleshooting-error-800b0100-cbs-e-identity-mismatch-during-service-pack-1-installation-on-windows-7-or-windows-2008-r2.aspx

--Joseph