While Mutter should reach version 2.30 with the release of GNOME 2.30 at the end of next month, this evening the Mutter 2.29.0 release has entered the world. This new version of Mutter offers improved appearance of scaled down windows using mipmap emulation, new signals and properties, merging of Metacity changes since the 2.26 release, and many fixes (for crashes, build, and bugs)...
Is OpenGL support optional? Can you turn off compositing, when on battery power, or is Mutter a compositing-only wm like Compiz?
2) No and you should not need to do so, if the compositor eats more power it is broken and needs to be fixed (ideally when using a cm it only redraws the parts that changed on screen so it should use _less_ power)
3) Yes a non composting mutter is metacity