I have a couple responses to this syndrome.
First, a drinker should NOT be consuming anything alcoholic without knowing exactly how potent the concoction is. As a rule, the more potent a beer is, the more expensive it is and the smaller the serving glass should be. There's a reason a Belgian or "extreme" beer (usually) costs a lot more than a "normal" beer, and it isn't just the cost of shipping or the bar's success in gouging consumers. "Big" beers cost much more to make than regular beers, and the actual profit margin on big beers is usually smaller than it is for mass-market beers. (Trust me on this: what keeps the bills paid at places like Max's and Brewers Art is not the big beers, but the sometimes-obscene mark-ups on mixed drinks, spirits, and the like.)
But therein lies the second part of the dilemma: Bars have a dual responsibility to both inform the consumer of the alcoholic level of a beer or other drink (provided it's not out of the ordinary--we should expect a wine to between 11 and 14% by volume and a whiskey to be around 40% or 80 proof) and adjust serving sizes accordingly. Any bar that is pouring 9% beers into typical shaker tumblers (which usually hold 12 to 14 ounces at best, in spite of the "pint" name--and that's a whole 'nuther post) is doing a disservice to the patron. Many "responsible" beer bars and brewpubs will post the actual alcoholic content in alcohol by volume either on the menu (see Brewer's Art, Max's, Wharf Rat, etc.), or on a chalkboard or other signage (Racers Cafe, Ellicott Mills, DuClaw, the late Capitol City Brewing-Baltimore). A few brewing places still inexplicably hide behind "original gravity" in degrees Plato, which doesn't help unless you know the relationships between original gravity, final gravity, and fermentation.
But one final challenge awaits some drinkers. Federal law requires the alcoholic content to be listed on the label of any wine or spirit sold in the U.S. But it's not only NOT required of beers, but in some jurisdictions, the listing of alcoholic strength was, and maybe still is, expressly prohibited on beer! To quote the FAQs of the old newsgroup rec.food.drink.beer:
When Prohibition ended, a statute was enacted that prohibited the alcohol content from appearing on beer labels unless required by state law. Nor could they use words like "strong", "full strength", or "high proof". Coors recently challenged this law in court and has won their lower court battles. However, some states have regulations that require certain beers to be labelled using other terms that are supposed denote strength without violating the above statute. Consequently some beers are labeled ales, even if they are lagers, due simply to their strength. Texas is one example of this usage. Similarly, "malt liquor" is the appellation attached to strong beers in other states, such as Georgia. Barley wines are strong beers, typically at strengths comparable to wines (8% alcohol by volume and over). However, this is not just an arbitrary term for strength but the actual name of the beer style as well.
In April 1995, the U.S. Supreme Court ruled in Coors' favor regarding the placement of alcohol percentages on beer labels. Some of Coors' beer labels now include this figure and other brewers are following suit.
Most of the world measures alcohol as a percent of volume (abv). In the U.S., alcohol in beer is measured by weight (abw). Since alcohol weighs roughly 20% less than water, abw measures appear 20% less than abv measures for the same amount of alcohol. In Europe, beer strength tends to be measured on the basis of the fermentables in the wort.
Until recently, Britain used OG (original gravity), which is 1000 times the ratio of the wort gravity to that of water. Thus a beer with an OG of 1040 was 4% more dense than water, the density coming from dissolved sugars. You can generally take one tenth of the last two digits to estimate the percentage alcohol by volume once the dissolved sugars are fermented. In the example used, the abv would be approximately 4% (40/10 = 4%) Currently, British beer is being taxed on its actual %ABV rather that the older OG so you'll often find both displayed.
Continental Europe tends to uses degrees Plato. In general, the degrees Plato are about one quarter the last two digits of the OG figure. Hence, in our example above, the beer would be 10 degrees Plato. To get the expected alcohol by volume, divide the degrees Plato by 2.5.
Years ago, I read of a study conducted where scientists tested a group of drinkers who believed they were drinking alcoholic beverages when they were drinking non-alcoholic beverages. They promptly proceeded to "get drunk"--i.e. perform increasingly poorly in motor skills and cognitive thinking--at almost the same rate as regular drinkers. If anyone has any idea where I/we can find that study or a similar one for review, let me know.