I leave Bluetooth on on my curve 24/7. I turn the Headset off when not using it, but leave it on on my phone. I have not noticed any difference whatsoever in battery life.
I leave the bluetooth device setting on 99% of the time.
I keep the ear piece power off unless I am using it.
With the devices not paired I don't see a significant battery drain.
YMMV
I typically charge every 2 days
Same as Eight_bit and jmatteau - always have it turned on and have never noticed any drain. If it's not connected to another device it's not going to use any noticeable battery power. The apps to worry about are those that use the cell radio - AIM, Facebook, etc. They periodically poll for updates and do wear down the battery.
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