Here’s the short list of “minor changes” to Windows 7 he found in a bootlegged version of a near-complete version of the upcoming service pack:

• Updates to Remote Desktop Services: required to accommmodate server-side changes known as RemoteFX for Windows Server 2008 R2.
• Improved third-party federation services support: improvements to the MS Federation Gateway Service (which lets users employ Live ID credentials and authentication on third-party sites) to support the industry-standard WS-Federation passive requestor profile (should make Federation Services easier and more reliable to use).
• Better HDMI Audio: Bug-fix for the small number of users who experienced disruption in HDMI audio following a system reboot.
• XPS document tweaks: Bug-fix for issue in documents that include both portrait and landscape pages that did not format print output correctly.
• Hot-fix/bug-fix rollup: All Service Packs routinely incorporate all previously released and new hot fixes plus bug fixes to establish a new, consolidated baseline for OS runtime code. Windows 7 SP1 does this, too.

Thurrott also reports that SP1 installation took over 40 minutes on a quad core Core 2 Duo PC, and that the Windows 7 build ID changes from 7600 to 7601 once the process completes successfully. Though there’s been no hint of install issues with SP1 for Windows 7 from any sources I’ve followed so far, remember to make a complete image backup of your system before installing SP1, and be sure to have an alternate boot/restore tool at hand. That way, if something does go kerflooey, you can use the boot/restore tool to restore your image and come away not too much worse for the wear. It can be difficult to roll back from a service pack install, and if the install fails at any time prior to completion and clean-up your system may not be bootable or working. You’ve been warned!