As it is with almost every poker question.....it depends.
As a rule, I like to have a few beers when I play, but I won't go out of my way for them. I've noticed that I don't usually drink when in the local rooms. I think most of that is because I just don't normally drink mid-week anyway - it's not really because I'm worried that 3 or 7 cocktails will affect my game.
When in Reno (et al) where the liquor is "free" and I don't need to worry about driving, I'm usually pretty liberal with the intake, but I don't get stupid. A drink/hour or so. I have a pretty high tolerance for liquor, so I'm able to keep my wits about me pretty well (well enough for a 3/6 game) and it loosens me up (attitude, not card wise) just a little.
I know that every poker "expert" in the world says that even one drink is too many, but I think sobriety is for those who can't handle their liquor. There has been an occasion or two that I have decided no to sit down because of severe intake (15-25 mega-cocktails over the course of about 12 hours), but even then I was sober enough to make the decision not to sit down.
You'll notice that I tend to have 3-6 beers (or beer typ drinks) during a BYOC event. Dealing has a greater effect on the amount consumed rather than any other factor.