Looks like it was rolled out very quietly! I just picked it up today while reinstalling one of our PCs.

Published 2/22/11

Windows 7 Service Pack 1 (SP1) is an important update that includes previously released security, performance, and stability updates for Windows 7. SP1 also includes new improvements to features and services in Windows 7, such as improved reliability when connecting to HDMI audio devices, printing using the XPS Viewer, and restoring previous folders in Windows Explorer after restarting.

What's Included in Windows 7 Service Pack 1 [windows.microsoft.com]