GNOME 2.30 will soon be released and the changes that Metacity 2.29.1 brings are simply bug-fixes, two new functions, and build fixes. The biggest change though is support for Clutter 1.2 and a dependence on this newer version (rather than Clutter 1.0 that was released last year) of the Intel-sponsored toolkit that's becoming an important part of the GNOME 3.0 stack. Clutter 1.2 was just released earlier this month with COGL enhancements, animator class improvements, layout managers, better documentation, and performance improvements.
The Mutter 2.29.1 release announcement can be found on the GNOME mailing list. Mutter is getting beaten into shape for its proper debut with GNOME 3.0, which is planned for release in September, but Mutter 2.29.1 will work with the current GNOME 2.29/2.30 stack. Likewise, the GNOME Shell and GNOME Activity Journal / Zeitgeist have been progressing along well too, which are other important components for the GNOME 3.0 desktop.