I've been using whey protein for a long time, off and on, and have always gotten positive results with it. Its a non essential protein that enhances your body greatly. It can be found in a body naturally, but it becomes depleted in individuals whom are heavy in weight training or endurance training.
Its not a supplement that will increase your muscle size or strength drastically, but it does give you that extra edge when it comes to recovery and muscle fatigue. For me, its a core part in my supplementation routine. No need to really cycle it either and given the amount you get for the price, its very realistic for the avg. to take this stuff year round.
For lifters, I suggest looking into complimentary supplements as well. My preference is cycling with whey and MMP; Muscle Maxx Pro + FREE L-Arginine (Nitric Oxide Booster) 250 Grams. It contains another one of those nonessential amino acids and it plays a pretty big role in nitrogen balance and metabolic processes - which translates into a massive amount of blood being shot into your muscles once contracted.
I train a lot longer and hardly ever got that lactic acid burn on arm days, at least it takes a heck of lot more to phase me. Even my cardio is easier on it too. I'd recommend it along with glutamine any day of the week specifically because it is actually partly synthesized from glutamine which means taking them together increases effects across the board.