The main thing about any "spirit" glass is the fact that you have to be able to get your nose into the glass. The human tongue can only taste sweet, sour, bitter, salt and sometimes unami or savory. All other "tastes" are perceived by your sense of smell. And everyone's sense of smell is different; that is why some taste certain flavors in booze, get grossed out by broccoli, cigars, or baby diapers.
When wine tasting, and I'm sure the same for anything else, is to have the item at the preferred temp. For dry red wine, it is 60-68 degrees. You pour liquid into the glass no higher than the widest part of the glass, and swirl. Take a sniff of the aromas with your mouth open, then swirl some more. Then take a sniff and a sip. Sniff and repeat.
This also depends if your palate is clean... that is, you haven't had anything sweet before a dry liquid, or a sour substance before a sweet. Think orange juice after brushing your teeth......yeeech!
Cold drinks should be served in stemware or heavy glasses so the heat of your hand doesn't warm the drink and drive the subtle aromas out. Beers should be served accordingly with a slight foamy head to release the aromas. Conversely, red wines, liqours can be put in stemware, but should be held by the bowl to warm the liquid and release the aroma.
A neat trick to prove these points are to have someone hold their nose/close their eyes while a jelly bean of an unknown flavor is placed upon the tongue by an associate. They will only ascertain the salt, sweet, bitter, sour or unami flavor.
The choice of glassware is widespread, and those of a certain shape marketed by a particular spirit maker, may be to enhance the particular flavors that that liquid is known for. So yes it is marketing and scientific.
I will try to find a Youtube video link by Barbara Stuckey given to a Google Friday seminar about tasting, years ago. I found it quite interesting.
