Microsoft has just released an RC version of its upcoming service pack. The version, windows6.1-KB976932, has been officially released and this may have been done because of the recent leak.
The SP1 will provide several enhancements to Windows 7 including Remote FX and many incremental updates to the platform. The SP1 can be found here and weighs in at 865.4MB for the 64 bit version and 514.7MB for the 32 bit version.
Microsoft releases service packs incrementally to make it easier for users to quickly bring their OS up to speed with all of the latest security patches and enhancements. Occasionally, Microsoft will introduce new features in service packs. Service packs are always provided free of charge, provided that you have a genuine copy of Windows.
As this release is an RC, a release candidate, it should be a stable version of the service pack, but as with any software that is not the final release version, install at your own risk.