There are no beer songs in the folk lore, but this doesn't mean there's no beer tradition. There's a brewery which is older than Guinness. The beer is European style, generally of Pilsner class. Before living in the US, I thought Serbian beers were mediocre at best; then I changed my mind.
The problem of quality is just the same as with any other product - it goes through three phases. First they do it right, to gain a name and a market. Then the market responds with demand, and then they drop the quality - hyperproduction does that. Then the market realizes it's not the same product anymore, demand drops, and the production stabilizes at some level where the quality is rather good.
I've heard it said that the best local beer is the one that's always equally bad. The beer drinkers get used to it and learn to love it. Just don't change it - they are the creatures of habit. If it gets better, they'll be deurinated when it goes back to normal. If it gets worse, they may not even come back to it when it gets better. The word doesn't get around so fast.
The traditional size of beer was 0,5 liters; international cafe scene has pushed this down to 0,33l, and now the frequency of both on the shelves is about equal. The new 2l bottles are gaining popularity (although many beer connoisseurs say that the plastic kills the taste), they are called "mason beer", because it's the favorite format for a moba. Alternate name is "krmača" (big, piglet-bearing swine).
Many supermarkets, maybe not downtown but rather in the suburbs and villages, won't mind if you take your beer out and drink it on the spot. Specially in villages they may have a bench in front (but then, almost every house has one, and these shops are usually in converted ordinary houses) where you can sit and drink. Often people do this after doing some physical work, like masonry, loading a truck or field work. A contributing factor was the kaucija, i.e. the price of the bottle itself - if you don't take it far, you often don't have to pay it, a promise that you'll leave it on the spot is enough.