Lots of new updates with this OS upgrade. This is important: PowerPC-based Macs will restart twice, instead of once, after the initial installation. Also, If you use iSync, you should perform a full sync with your devices before installing this update.

Fixes include: login and authentication in a variety of network environments; file access and byte range locking with AFP file sharing; network access when using proxy server automatic configuration files; connecting to Cisco VPN servers using IP/Sec; using Bluetooth wireless devices; searching iWork ‘06 and Microsoft Office documents with Spotlight; saving Word documents automatically when using a network home directory; creating Automator workflows for iPhoto 6; synchronizing contacts and calendars to .Mac and mobile phones; mounting and unmounting iDisk volumes; compatibility with third party applications and devices; and previous standalone security updates.

All of the docs can be found here. Download it via Software update today.