Earlier today the Exchange team released Update Rollup 6 for Exchange Server 2007 SP3.
De following list calls out the most important fixes which are included in this release:
22656040 An Exchange Server 2007 Client Access server may respond slowly or stop responding when users try to synchronize the Exchange ActiveSync devices with their mailboxes
2498852 "0x80041606" error message when you perform a prefix search by using Outlook in online mode in an Exchange Server 2007 environment
22653334 The reseed process is unsuccessful on the SCR passive node when the circular logging feature is enabled in an Exchange Server 2007 environment
22617784 Journal reports are expired or lost when the Microsoft Exchange Transport service is restarted in an Exchange Server 2007 environment
2289607 The week numbers displayed in OWA do not match the week numbers displayed in Outlook for English users and French users in an Exchange Server 2007 environment
For the complete list check HERE
Note for Forefront Protection for Exchange users For those of you running Forefront Protection for Exchange, be sure you perform these important steps from the command line in the Forefront directory before and after this rollup’s installation process. Without these steps, Exchange services for Information Store and Transport will not start after you apply this update. Before installing the update, disable ForeFront by using this command: fscutility /disable. After installing the update, re-enable ForeFront by running fscutility /enable.