From Microsoft:

Today Microsoft is releasing Service Pack 2 for the 2007 Microsoft Office system. This service pack delivers significant stability, performance and interoperability improvements for customers, including additional file format support, and offers enhancements for Microsoft Office Outlook, such as improved calendaring reliability and general performance.  To download Office 2007 SP2, visit the Microsoft web site.  Please note that SP2 will be available for download starting around 11 a.m. PDT.

(It's available now, I just grabbed it.)

The enhancements in SP2 span across the servers and software applications that home and office workers rely on daily and make the 2007 Office system an even more effective productivity tool.  Service Pack 2 also makes interoperating with Office easier for developers by providing tools and resources to make the development process shorter and more cost effective.

More info:

The 2007 Microsoft Office Suite Service Pack 2 (SP2)

The 2007 Microsoft Office Suite Service Pack 2 (SP2) provides customers with the latest updates to the 2007 Office suite (the products that are affected by this update are listed below). This download includes two types of fixes:

Previously unreleased fixes that were made specifically for this service pack.

In addition to general product fixes, this includes improvements in stability, performance, and security.
You can find out more information in Knowledge Base Article 953195, where product-specific changes are described.

All of the Public Updates, Security Updates, Cumulative Updates, and Hotfixes released through February 2009.

Before installing this service pack, you are strongly encouraged to read 953195, which describes some big improvements introduced by SP2, and also calls out some important information that you should be aware of before installing.

Office Service Pack 2 A Significant Stability, Performance and Interoperability Upgrade

Q&A: Group Program Manager Jane Liles talks about the enhancements now available through Service Pack 2 for the 2007 Microsoft Office system.

Working with ODF in Word 2007 SP2 (blog post)

Office 2007 Service Pack 2 Kiosk (blog post)

UPDATE: Colin M. mentioned via email that Visio, Project, SharePoint Designer, and Office Servers have separate SP2 downloads. These are:

Visio

Project

SharePoint Designer

Office Servers