Drinking is done from a drink container (barrels, pots and waterskins/flasks/vials) and takes place wherever the drink container is, there's no location requirement for drinking, which means it's usually at the still or in the drinks stockpile or wherever the last boozehead dropped a barrel. (Water can be drunk from wells, open bodies of water or when given water from a bucket.)
Eating takes place at the nearest available _chair_. Dwarfs who own a chair, e.g. in a personal dining room, but also in an office, will use such a chair when it's currently free and dwarfs will not use a chair owned by someone else. Other than that, every built chair is fair game.
Only after having planted their butt in a chair will dwarfs check whether there's a table within reach - and complain if there isn't or if the table's already in use by another dwarf, sitting in another chair adjacent to the same table. Having more chairs than tables is therefore a bad idea, since dwarfs don't establish beforehand if they have a decent setting for their meal and only check appropriateness after they've sat down. Having more tables than chairs is no problem, tables without adjacent chair just won't be used for eating.
PS: making drinking a more social activity sounds very dwarf-like to me and i'm certain it's been suggested. It may even be part of Toady's to-do list already, as the "tavern" idea.