The Daily Mail reported over the weekend that less than a third of people paid any attention to the strength of alcohol they drank at home. However, the article fails to build up much of a head of outrage, as surely what this indicates is not that drinkers are unwittingly consuming more alcohol than they thought, but that they regard drinking as a more rounded pleasure and not simply a calculated way of getting a given dose of alcohol.
In any case, this only really applies to beer and cider, as the strength of table wine falls within a fairly narrow range, that of spirits even more so. And, even if people don’t know the exact strength of what they are drinking, they will still have a broad idea of the general category it falls within, in the same way as you probably don’t know the exact horsepower of your car, but you have a pretty good feel for how quick or slow it is.
It could even be argued that, if people are indifferent to the precise strength of their drinks, it gives brewers more scope for reductions in % ABV, but, as I have said before, they run the risk of losing sales if they are seen as having taken a particular product out of its perceived strength category.