Most prominently, GTK+ 3.2 will feature the HTML5 back-end that's dubbed "Broadway" and allows GTK+3 applications to render over the web to modern HTML5-supportive web-browsers like Firefox 4 and Google Chrome.
Development releases of GTK+ 3.2 have also brought in back-end improvements that will ultimately help the Wayland support, a major visual refresh to the GtkAssistant, GtkFileChooser remembering the last opened directory, a GtkLockButton with PolicyKit support, many bug-fixes, and other changes.
Announced this morning was the GTK+ 3.1.6 development release. This new GTK+ release introduces a GtkOverlay container for placing "overlay" widgets on top of another widget, such as for allowing support for floating status-bars and the like. There's also greater accessibility, a simplified GtkLockButton, the print dialog can display color profile information, various widget tweaks, and many enhancements to the CSS theming support. The CSS parser has been rewritten to comply better with the Cascading Style Sheets specification and to provide better error handling. This rewritten CSS parser also now supports text-shadow, box-shadow, icon-shadow, and other elements.
Read more in the GTK+ 3.1.6 release announcement on the GNOME mailing list. Due out on Wednesday is the GNOME 3.1.2 unstable release and more development releases every few weeks until the planned GNOME 3.2.0 release on the 28th of September. Read this article for some of the features that you can expect from the GNOME 3.2 desktop.