GTK+ 2.24 is the last stable GTK2 release in that series with all of the exciting work now going into GTK3, which will also be officially released soon. GTK+ 2.24 is the last stable update but it will continue to be maintained and receive bug-fixes. GTK+ 2.24 isn't too exciting but is a step to help in porting applications to GTK3 while still being source and binary compatible with earlier GTK2 releases.
GTK+ 3.0 brings a lot of exciting work like X Input 2 by default, better Mac OS X support, is more X11 agnostic and friendly with the Wayland Display Server, drops DirectFB, uses Cairo more for drawing, and has many other advancements.
Clutter 1.6 brings a Wayland back-end, generates GLSL shaders for describing the state of the pipeline, X Input 2 support, VBO (Vertex Buffer Object) support on OpenGL ES 2.0, clipped re-draws on EGL, and other underlying improvements.
The GTK+ 2.24 release announcement can be read on the gnome-announce-list along with the Clutter release message.