If you use FileVault with Mac OS X 10.6, decrypt your home directory before installing Mavericks, and then encrypt your entire drive using FileVault 2. See About FileVault 2 in the Apple Knowledge Base for details.
Boot Camp no longer offers driver support for Windows Vista or XP.
PowerPC applications do not run in Mac OS X 10.9. IU no longer distributes any PowerPC applications, but some users may still have older versions of software installed on their system (e.g., versions of Microsoft Office older than 2008); these will no longer work.
Symantec Endpoint Protection is not compatible with Mavericks.
Ozzy Musa writes from Minneapolis Minnesota and is a regular contributor to Techlivewire.com, a growing Tech, Gaming and how-to blog.