The release notes cover a plethora of changes that were introduced in the 8 series, though the most notable additions are software upgrades such as GNOME 2.20, KDE 3.5.8 and OpenOffice 2.3, along with the relatively new 2.6.23 kernel release. The download weighs in at around 3.4GB.
Update: In addition, the related Red Hat distro has just released the newest version of Red Hat Enterprise Linux. The new 5.1 release includes standard virtualization support and is clearly aimed at companies looking to begin deploying virtual environments en-masse. You can read the RHEL press release for more information.