The major new work to GTK+ 2.91.7 that caught our attention was the merging of the gdk-backend branch and the GDK X11 back-end usng XI2 by default. With the merging of the gdk-backend branch, the front/back-end separation in the GDK is cleaned up so that it will eventually allow a single GDK library build to contain multiple back-ends. In other words, the same GDK library could target both X11 as well as Wayland. Another common scenario would be targeting both X11 and Quartz for Mac OS X users. While this branch has been merged, the vision hasn't been reached quite yet for one build supporting multiple back-ends, but the rest of the work is forthcoming.
With the GDK X11 back-end in GTK+3, X Input 2 (XI2) is now used by default. X Input 2 is what brings multiple pointers to the X Server and many other changes. GTK+ 3 is fully supportive of the multi-pointer / multi-device capabilities and now this X Input 2 support is found "out of the box" for GNOME's tool-kit. Though programs can disable the multi-device support using a built-in command if they wish to use the traditional X11/Core implementation.
Other changes in GTK+ 2.91.7 include more flexible cell arrangements with re-factoring the tree-view code, deprecating and removing some parts of the GTK API, more GTK+ widgets have been ported to using GtkStyleContext, and there's lots of bug-fixes.
The release announcement for GTK+ 2.91.7 can be read at GNOME.org. The GNOME 2.91.4 release should be out later today. After that, the next development snapshot will come in the middle of January, GNOME 3.0 will go into Beta in late February, and this major Linux desktop overhaul should be officially released in March.
Other GTK+ 3.0 changes thus far include a rendering clean-up, becoming more X11-agnostic, greater support for the Wayland Display Server, an (unmerged) HTMl5 back-end, no more DirectFB support, and uses a lot more of Cairo.