Be sure to download and install it through Software Update. Word is that it fixes a lot of bugs, and I can already verify that it solves a few AirPort issues.
For MacBook and MacBook Pro users: if your Mac tends to lose your WiFi network signal after waking up from sleep, the update will fix that. So far I haven't seen my own MBP from dropping my network after sleep.
This update fixes numerous other issues as well, so be sure to get it.
-BMF

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