I'm finding that Voice Command is no longer functional (moves instantly to "Unfortunately, Voice Commands has stopped" on program start). That's been the default app invoked by a long press of the Bluetooth headset button. Clearing that default brings up a choice between Voice Commands and Google Search, whose robotic voice drives me nuts. Given the choice between irritating and non-functional, though ...
ETA: answered elsethread. Uninstalling the Google Play Music updates restored the functionality of Voice Commands.