There are no cure-all's in sports medicine-except for ice baths. When I first heard about them I tried it out dubiously, thinking that the benefit, if any, would be minor. Boy was I wrong.
You use an ice bath when you have done a really intense workout, when the muscles have been severely broken down. It's easy to know when you reach this threshold, because your muscles will be sore immediately after the workout, instead of kicking in the next day. I had one of those workouts today; after a couple of weeks of rest I did a fairly intense strength training session, and as I was reaching down to unlace my shoes afterwards, my legs were shaking. I knew an ice bath was what I needed.
The name "ice bath" is a little misleading, because the water doesn't have to be 33 degrees, it just has to be cold, significantly colder than your body temperature. I try to shoot for around 55-60 degrees. You fill the bath tub up with just enough water to cover your legs, then you sit down in it for 10 minutes. At this point you might be saying to yourself, "I don't care how good this is for you, there is no way I'm getting in that bath!" But it really isn't that bad; it's a shock right as you slide in, but after a few seconds the escaping heat from your body warms the water immediately around you and it just feels cool.
I'm a runner, so I've only worked my lower body hard enough to require the cold water. But you could ice your upper body if you wanted...it would just be a little trickier. For one, when your heart and lungs are submerged, that is when you really feel the chill. But if you kept the temperature moderate it shouldn't be too bad, and you could slide your whole body into the water and get the benefits all over.
So now we know the cost. What is the reward? First, the cold helps reduce swelling-whenever a muscle is injured (any strenuous exercise is a series of many small injuries) it swells, and getting past that swelling phase is necessary for recovery. Second, it helps your muscles get rid of lactic acid. The processes by which your muscles produce energy are complicated, but one of the by-products of high-intensity workouts is lactic acid. That leaden feeling you get in your legs near the end of a hard race is caused in part by the muscles being flooded with this substance. What the cold water does is it forces blood to rush to the legs, speeding up the removal of the lactic acid and other toxins. I follow up the ice bath with a hot shower, but not really for any therapeutic reasons, it just feels good.
The real benefit comes the day after. When you wake up, instead of feeling heavy and sluggish, your legs will feel lighter than air. You may still be a little sore, but it will be much less than if you hadn't iced. In my experience, it cuts recovery time in half, which means you can feel good quickly and get on to your next workout!