The X.Org 7.6 katamari (basically all of the independent X.Org drivers/libraries/modules and xorg-server tagged all together in one bundle) was in December of 2010. There were plans to do the X.Org 7.7 katamari in March with the X.Org Server 1.12 release in March, but now it's coming about one month later following the xorg-server 1.12.1 maintenance release.
Alan Coopersmith announced X11R7.7 Release Candidate 1 on the mailing list. "At this point, only some final bug fixes, documentation updates, and janitorial cleanups are expected between now and the final release of X11R7.7, including final releases of several modules for which release candidates are included in this set (including libX11 1.5.0 and xorg-docs 1.7.0)."
With X.Org being modularized and the various drivers generally being released at will on their own time-frame, major X.Org Server releases now making it out on time every six months (and point releases every few weeks), and lots of focus turning to Wayland, the X.Org "Katamari" releases have less priority and use than they did in the past.
There really isn't anything "new" about X.Org 7.7 but it's just pointing to all of the updated official X.Org modules since the 7.6 katamari in 2010. Many packages have been updated multiple times since the last katamari, while other packages like xf86-video-openchrome are stale.
This is also only official X.Org modules part of the katamari, so for example, xf86-video-nv is still part of the 7.7 package collection with xf86-video-nouveau having yet to do an official driver release. Additionally, for the key graphics drivers, the latest upstream versions generally only work on Linux "out of the box" due to Solaris and BSD lagging behind in KMS/DRI2/GEM/TTM support.
Among the many X.Org 7.7 packages are xf86-video-intel 2.18.0, xf86-video-ati 6.14.4, xorg-server 1.12.1, libXrandr 1.3.2, and libXi 1.6.0.
In more exciting X news, there's just about five months to go until the annual X developer summit taking place in Franconia.