Hmmm......there's that standup comic ridgeline again.............
Actually, he's right when it comes to a lot of the bodybuilders, but that's another story.
Ranboze, great questions. I'll try to answer them in a way that most can follow.
When it comes to metabolic recovery, we are talking first and foremost carbs. The first thing your body is going to want to do is get back to a positive energy balance, and that means replenishing the carbs utilized in the activities that were performed. With the exception of short sprints and limit or near limit lifting, carbs are the primary energy source for most activities. It is now well documented by science that the storage form of carbs in the muscle, glycogen, is replenished at a rate twice the normal rate in the first 2 or so hours right after exercise, so that would be a time you would want to get some carbs into your system to facilitate recovery. Carbs in liquid form are going to be the most rapidly available, whereas solid carbs in the form of regular food will generally take longer to digest and absorb, so this is the preferred form. It has also been shown that carbs + protein is absorbed more efficiently than carbs alone, and the best ratio for this is 4 carbs to 1 protein, which, incidentally, is the ratio in Endurox 4 and Accelerade, both developed by the late Edmund Burke, an Exercise Physiologist at the U. of Colorado who was also sports scientist for the U.S. Cycling team and I had the pleasure of meeting at one of the ACSM Research Conferences, where I attend presentations of the latest research.
As far as measuring recovery time, short of putting a person in a research lab and measuring such things as ability to achieve VO2 Max, RQ, or taking a muscle biopsy, it is hard to say when a person is completely replenished; suffice it to say that a well trained person on a proper diet aided by these types of supplements can expect to replenish in as little as 24 hrs, provided there is not much microtrauma to the muscle, which will increase the recovery time because it affects replenishment. Most athletes or their coaches have figured out over time where their recovery time lies. Of course a real easy way to figure out if you have recovered metabolically is whether you can do the same event at the same intensity as previously.
As far as physiological markers for structural recovery, microtrauma of the muscle fibers generally will lead to muscle soreness that typically peaks 24-48 hrs. following the event, hence the term DOMS or Delayed Onset Muscle Soreness. There has never been any documented evidence that active recovery, electrolyte drinks, stretching before or after, etc. will decrease muscle soreness or hasten the recovery time. Dehydration or lack of electrolytes may affect the degree of soreness, since muscle contraction is compromised; however, extra water or electrolytes don't make any difference. There is some evidence that certain types of protein will aid in the recovery time ie. repair of the microtrauma. What will help is conditioning such as the activity itself or something such as resistance training, and hormonal manipulation.........like steroids!
In terms of aiding recovery, nutrition of course is important (I'm not mentioning sleep-that's a given for ALL types of recovery) with carbs being important. Protein, of course, is important as well, but more so during the start of a new program as the body adapts by building more muscle. Generally a recovery supplement will have a higher ratio of protein in it as compared to the ratio found in an endurance recovery drink. Studies have shown that protein feedings before and after working out will aid in the growth of the muscle compared to just eating regular meals at regular times.
How do you know you're recovered? Well, if you do your activity again and you're still sore, you are not fully recovered, and, no, you can't work the soreness out, no matter what any pseudo-trainer might tell you. A more subtle way to tell is if your mechanics are different, or you start feeling aches and pains somewhere else while doing your activity; this may be a sign that your body is trying to compensate for muscles that are still not recovered.
The last type of recovery, of the neuroendocrine system, is a little more difficult to accomplish, because if you have overstressed this system, you are in an overtrained state. Severe overtraining will lead to what's called parasympathetic overtraining; see Kathy's first post if you want to know what some of the symptoms are. When you are at this point, you have to let your body rest and replenish, and, at least in terms of legal methods, there's not much you can do; this can last for weeks and even months. Nutrition will only help to a small extent at this point.
There are a number of ways to determine if you've reached this stage. The easiest way is to know what your waking heart rate is. If your HR is 3-5 beats or more above what it normally would be, you are potentially in an overtrained state and need to back off your training or activities in order to let your neuroendocrine system recover. Changes in sleep habits or time, mood swings, changes in appetite, and constant fatigue are also signs you may be in this stage.
Sorry for the long answer; I could actually go into more detail.
Hope this helps answer some of the questions.