I drink 3 / day. I'd rather drink 1 or 2, and get the rest from a real meal. But I don't have that kind of time. A smoothie for breakfast w/ 3 servings of fruit and a scoop of protein, and some fat free yogurt w/ active cultures. Run out the door and drive to work while drinking it. Saves me a good 10-15 minutes in the AM.
At work, I'll drop another scoop of protein in some water and drink that mid-afternoon (2-3 hours after lunch). Dinner when I get home, and another smoothie before bed with some other combo of ingredients so I don't get bored to death with smoothies / protein drinks. If not for this, my caloric intake would not be enough to support new muscle growth. Hell, it still might not be.
Make sure you rest, bro. One of my recent epiphanies was that I was not taking enough days off between workouts, not sleeping enough. Just because you split your muscle groups doesn't mean you're getting enough rest. Even if Monday is chest / tris, Tuesday back / bis, Wednesday legs, and so on --- remember, every day is liver day, kidney day, pancreas day. Your internal organs have to repair all the damage you're doing by breaking down your muscles. Make sure they get enough rest, too.
Results of resting more and eating more: I have gained about 10lbs in the past 3 weeks. I *hope* it's all going muscle. Pretty sure it is. Waist size hasn't changed. But shirts are tighter on shoulders / arms and shorts tighter on thighs. I can't wait to update my pics. They're all 10-15lbs ago.