it's a continuous work in progress - remember: the GNOME 3.0 release is planned for April 2011.
generally, you want Clutter 1.6.4 (which is the latest stable release), as the fixes for performance issues regarding the scene and redraw almost always end up being bug fixes there. Mutter is pretty transparent, so you should only update it when GNOME Shell requires a new version because of changes in the internal API.
next week there should be the first, UI frozen beta release of GNOME 3.0; my suggestion is to try it then.