Nick White over at the Vista team blog just announced that RC of Vista SP1 is going on Microsoft Connect today and to MSDN and Technet subscribers tomorrow. It will then go public next week. The highlights:

• The size of the standalone installers have decreased significantly. For example, the standalone installer packages consisting of all 36 languages (x86 and x64 chip architectures) are smaller by over 50%. The standalone installer packages consisting of just the 5 languages (again, x86 and x64) slated for initial release are more than 30% smaller in size.
• The required amount of disc space for SP1 installation has also decreased significantly. Furthermore, with the RC, if more space is required to install SP1, an error message will now display exactly how much space is needed to complete the installation.
• Previous SP1 versions left behind a directory of files that wasn't needed after installation and occupied about 1GB of space; the RC includes automatic disk clean-up to remove this directory.
• Installation reliability has been improved based on bug reports and error codes reported from Windows Update (thanks, Beta testers!). Testing shows that these improvements have significantly increased the proportion of successful installations of the RC.
• We've improved the user experience of installing SP1 via Windows Update. During the Beta release, users installed without much guidance from Windows Update. The RC now contains a series of screens with detailed information on SP1.

I've been running an RC build for a while now and VERY happy with it. Go get it folks!