After installing Mavericks my late 2012 Mac Mini power light no longer pulses when the system is put to sleep; instead it just resolutely glows at normal operating brightness, refusing even to have the decency to dim itself! It was definitely pulsing the night before the upgrade as I was staring at it as I went to sleep..
Edit - it's not the end of the world, as otherwise 10.9 seems very very good.
Edit - it's not the end of the world, as otherwise 10.9 seems very very good.