Mac OS X 10.6 will no longer be supported in patch 5.2, so if you happen to be running under that operating system, you may want to consider upgrading. While World of Warcraft has long been known for running on ridiculously outdated computers, it has over time dropped support for older operating systems. Does this mean you can't play if you're running OS X 10.6? Nope -- but it means it will no longer be supported, so if your game suddenly stops functioning correctly with that operating system, there's not much to be done about it other than upgrading your OS.
There is no need to panic if you're currently running with said operating system, however -- your game isn't going to suddenly stop running tomorrow. Daxxari posted more information about the changes, as well as some helpful links to follow as a polite heads-up warning in advance, so players using this OS will have time to make any changes they need.
In the upcoming Patch 5.2: The Thunder King, players using Mac OS X 10.6 will be presented with a message stating that we will no longer support Mac OS X 10.6. During this time, you will be able to continue playing; however, Mac OS X 10.6 will no longer be supported. We recommend Mac users upgrade their systems to Mac OS X 10.7.5 (or newer) as soon as possible.
We are giving players advance notice of this change to ensure Mac users have enough time to update their operating systems in preparation for the release of Patch 5.2: The Thunder King. We will provide an additional update when we no longer provide technical support for Mac OS X 10.6. Mac OS X 10.7 and Mac OS X 10.8 will continue to be fully supported per the recently posted Mac OS Support policy here. For more Mac-related information and help, visit the support site.