We are doing a pretty quick turn of the crank on VS 2013 Update 1. Originally we were thinking our first Update would take a little longer but for a variety of reasons (most prominently the feedback about VS supporting versions of IE before IE 10), we decided to do a quick initial Update focused on just some key bug fixes. Our first significant "feature Update" is still planned for the first half of 2014.
You can download the RC here: http://www.microsoft.com/en-us/download/details.aspx?id=41204
You can read the KB article (including the list of fixes) here: http://support.microsoft.com/kb/2911573
This is a "go-live" RC so it should be safe to install in a production environment and it will be fully upgradable to the final release of Update 1.
Read more: Brian Harry's blog