The Fedora Project has announced the release of Fedora 9, codenamed "Sulphur". As your periodic table will tell you, Sulphur is the element below Oxygen, a fitting release name for the third major distribution to ship KDE 4.0 (congrats to Mandriva and Kubuntu for getting there first) and the first to make it the only version of the desktop. Fedora 9 includes KDE 4.0.3. Unfortunately, KDE 4.0.4 was released too late to make it in, but there is no need to despair, it is already available in updates-testing and is expected to become a stable, tested update in a few days. To support your existing KDE 3 applications such as Kontact, Amarok and K3b, Fedora 9 includes compatibility libraries from KDE 3.5.9. As always, the KDE Live CD is installable. New in Fedora 9, the live image can also be converted to a persistent USB key. The release notes have a section dedicated to KDE 4.
In addition to the inclusion of KDE 4 as the default KDE, Fedora 9 also comes with other major new features, such as the switch to Upstart to handle system startup, an improved NetworkManager including support for mobile broadband and systemwide configuration, a new, fast version of X.Org X11, TexLive replacing tetex, unified spellchecking dictionaries and much more.
If that was not enough to convince you, you can have a look at some screenshots showing KDE 4 on Fedora 9. (The first few screenshots are of the installer, so scroll down to see the KDE ones.)