(Note: info on the release version of Windows Vista Service Pack 1 is available here. This article discusses whether or not you should install a service pack directly from the Microsoft Download Center or wait for installation via Microsoft Windows Update.)
We've installed the RC on all PCs at home (and of course, at the office 😉 and found that it provides greater stability, improved reliability with support for more devices, and more.
But should you install it?
If you're evaluating Vista for corporate or enterprise deployments, a computer enthusiast who likes taking on the latest software and technology, or are comfortable with release candidate software, then yes, by all means. (Note that this is not for production environments - and always make a back up.) Assuming that you are a regular MSDN reader, than this RC's for you to evaluate and put through it's paces. We've been using the release candidates with great success at home and at work, and found it to be solid.
But... If you are a consumer who would rather that Windows Update handle all the heavy lifting for applying the latest updates and patches, then you should carefully consider installing a release candidate package. Windows Vista SP1 RC Refresh is pre-release software and as noted on the download page "will change before the final release."
Windows Vista SP1 RC Refresh is for individuals, organizations, and technical enthusiasts who are comfortable evaluating pre-release software and is provided for testing purposes only. Microsoft does not recommend installing this software on primary or mission critical systems. Microsoft recommends that you have a backup of your data prior to installing any pre-release software.
Also note that this RC is time-limited software and will not work after June 30, 2008, requiring it to be uninstalled before it turns into a pumpkin.