[Milhouse]

In noob terms...does this bluetooth audio thing mean that I can plug in a USB bluetooth dongle to my Rpi2 and listen using BT headphones?

Yes, although this facility will not be available in build #1111b:

1. Install your Bluetooth dongle in your RPi/RPi2
   
2. Pair it with your Bluetooth speakers/headset using the OpenELEC Settings add-on
   
3. Execute the following in ssh (you'll only need to do this once). Enabling snd_bcm2835 is required to enable the ALSA/Pulse bridge.
   
   Code:

   echo snd_bcm2835 >/storage/.config/modules-load.d/snd_bcm2835.conf
reboot
4. In System -> Audio, select "ALSA: PulseAudio Sound Server" as the audio output device
   

Once you've successfully configured the above whenever your Bluetooth speakers or headset is connected you should hear audio over Bluetooth, and when they are disconnected you should hear audio over HDMI.

It's not yet perfect, and lag/latency can be a bit of an issue, but it's generally working and should be considered a "work in progress".