I am actually shocked at the replies and the expectation that the wedding hosts will pay all night to get anyone sloshed (should that be their intention). Perhaps this is a very very regional thing, or a financial bracket thing? The bar bill could be quite costly.
I always...ALWAYS...expect that I will have to pay for any alcoholic drinks. At just about every wedding I have been to, the hosts will provide toasting bottles of champagne at each table (or waitstaff circulating with them..whatever is left...when its gone, its gone), free soda's all night...and usually a few kegs (when its gone, its gone sort of thing). Alot of time, they could do the free bar up until dinner is served, or some other hour or so time frame frame perhaps. But very very rarely ahve I been to a wedding, fancy or not, where there was free booze all night long.
The most likely to have free booze would be a more down home, do it yourself wedding...but that would be where they bought the keg or the boose...no mixed drinks but stuff in bottles (Mikes Lemonades, etc).
JMO...and my experiences...
I just assume its cash needed and we hit the cash machine before we go or the day before, as we rarely have cash. Part of our wedding routine!