The Release Candidate (RC1) for Windows Vista's Service Pack 1 (SP1) has been released to beta testers today. The build for the SP1 is 6001.17042 and can be downloaded from Connect. I found an email from Microsoft about the release and is available to download, after you click on the invitation link.
A lot of people have been waiting for Service Pack 1 (SP1) for the adoption of Vista. For a lot of people service pack 1 means a lot since they feel Vista is not very stable and feature-rich at the moment. I personally think Vista is pretty stable and Windows Update has been doing a pretty good job. Vista SP1 does not bring any major feature like SP2 did for XP. Instead, SP1 is more about the fixing the compatibility issues and improving performance.
According to Microsoft, it has been released to "15,000 pre-selected testers". But it's not yet known when they are going to release the public version of SP1. All signs were towards a Dec, 2007 release, but now it seems it'll be only in Jan, 2008 that we are going to see the release. Also other tricks on Windows Update to get Vista SP1 as mentioned here, aren't the real SP1, since quite a lot of changes have occurred after that!!