My company is family run and managed by the three founding brothers. They have a reputation as party people (by which I do actually mean they throw great parties - juglers adn fire eaters at the last one).
There is an expectation that one will drink to excess in middle management, and the founders certainly drink their fair share at a party, but it's interesting to note that when they are talking in private, the founders will castigate staff that got hopelessly drunk in their presence.
It seems that having a drink is not expected, but if you choose to do it, you'd better be able to carry it off.
I have a few, and switch from large beers to mixed long drinks early on, and as said above let people assume that there's gin in my tonic...
