One band I was in, we played clubs about twice a month and parties pretty the rest of the time. A the clubs, we each had at most 2 beers during the night and we would generally share a joint or 3 sometime during the evening.
At the parties, which were usually at someone house. We had a beer between\during each set. We never got ****faced unless the party went past say, 3am (usually the police were there before then :)).
The only real problem we had was our drummer. He could drink beer all night long and still keep a good beat. But, once he got ahold of hard booze (JD etc.) his timing went to hell. BAD. One weekend, we had no gigs going on so we went around town to see other bands playing. We went to this one party (wedding reception actually). We knew the band playing there and got them to let us do a set.
Afterwards, some guy offered us $1000 to do another set!
Unfortunatley our drummer had already found himself a bottle of Jack, so we had to decline. The rest of us were very pissed.

As long as you can keep in in moderation, there should be little problem with it.