Ubuntu 13.04 has delivered many new features to this popular Linux distribution with many of the prominent user-facing changes being noted in the many Phoronix articles up to this point, including many performance tests that have been done in the past couple of months with Ubuntu Raring development snapshots.
Among the items Canonical is promoting is the Unity desktop performance improvements, updated core and toolchain components, a new Friends service through Ubuntu Online Accounts, a technology preview of Upstart's new user session feature, Ubuntu Server updates, and much more.
Kubuntu, Xubuntu, Edubuntu, Lubuntu, and Ubuntu Studio are also doing their 13.04 releases today too. Additionally, with 13.04, Ubuntu GNOME and Ubuntu Kylin are part of the family.
More details to be found within the mailing list announcement.