The Exchange Server 2007 SP3 bits are now available for download. The accompanying documentation includes: Release Notes and What's New in Exchange Server 2007 SP3.

As highlighted in the EHLO blog post Ask and you shall receive - Exchange 2007 SP3 w/support for Windows Server 2008 R2 Now Available  this service pack was created in response to strong customer demand for Windows Server 2008 R2 support for Exchange 2007. In addition to the newly supported OS, this service pack also provides updates to a number of core components and the re-introduction of the password reset functionality within OWA for customers using Windows Server 2008 and Windows Server 2008 R2.