On every SBS on which I’ve installed KB958644, the server restarted with no network connectivity. If you have installed it, uninstall it and decline future offerings of it.
Edit: Though the problems with this patch were revealed shortly after its release, it is important to install this patch. In my experience, the problem is that IPSec fails to start with, “The IPSEC Services service terminated with the following error: Only one usage of each socket address (protocol/network address/port) is normally permitted. “
Just be sure to do it when you’re on-site so you can make these changes: http://support.microsoft.com/kb/956189