For the last couple of releases of OS X, there have been some parts of the OS and the utilities that have been simplified or removed compared to the previous release. Especially as seem from a power users point-of-view.
Two examples from past releases are the scaled down AirPort Utility (version 6.0) and the limitations in "Sharing" System Preference panel that used to be able to manage FTP servers - both changes have been rather annoying in my book!
So, before I "upgrade" to Mavericks, I would like to know if there are anything specific that will be "downgraded" in the same process.