BA recognised the problem 4 or 5 years ago. The figures I saw suggested that on the 747-400 using the one ear off method of wearing the headset meant that the volume had to be circa 12 dB above ambient to hear effectively.
It was found that hearing loss was being caused in the headset ear for this reason.
The company now fit Sennheiser ANR headsets to all fleets and intercom is SOP for all fleets with a couple of minor variations.
Two interesting observations on the 747-400 many refused to use the intercom and continued to use one ear off because 'it was a short-haul/BEA idea' (1-11s and I believe Tridents used intercom)! Also the 777 flight deck is so quiet that one ear off is rumoured to be comfortable and also more sociable as a spin off.
I fly the 757/767 and the headsets are a very good considering the appalling ambient noise levels on some of the 757s. I find my volumes are set to minimum most of the time. HF is also easier with both ears covered using an ANR headset.
The headsets are slightly anti - social in that when the CC come in one has to remove one earpiece to converse. They are also very expensive, circa £400 I believe.
I care about my future hearing and carry small ear plugs for use in nightclubs down route and wear ear defenders when using a hammer drill etc at home. I suspect that many youngsters today are storing a whole load of trouble for the future with our penchant for deafening music volumes in the car, nightclubs etc. I may look a pratt but at least I will be able to hear you telling me!