Fedora 18, the Spherical Cow, has hit some delays over the past month or so, with the remaining development versions being pushed back by over a month, leaving the final release to be delayed into 2013. The troubles have subsided though, and the Fedora Project has seen fit to release the Beta of Fedora 18.
Fedora 18 Beta comes with GNOME 3.6 by default, for better or worse, although as well as updates to all the other available desktops, MATE has finally been added to the official repos. The anaconda installer has been upgraded, and there are a number of updates to Samba, OpenStack, Eucalyptus, and more.
You can get the Beta from the Fedora download page. The current release date for Fedora 18 is 8th January 2013