The Science of Semen

I've heard the "semen = protein" statement so many times I thought I'd educate myself on it and find out the truth to this "oh so amusing" concept. [This is strictly for educational purposes]
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From Yahoo! Answers:

Semen actually contains very little protein. The proteinaceous material in semen would be whatever proteins were contained in sperm cells and a few clotting proteins (the stuff that makes semen sticky and gooey). For the most part, semen is water. If you dehydrated the water, then the next biggest component is zinc. Also, you have a lot of citrate, sodium bicarbonate and fructose. Don't remember what the fructose was for. Citrate feeds the sperm cells. and sodium bicarbonate neutralizes the urethra and vagina. Also, you polymerized amines (nitrogenous compounds), which give semen its characteristic scent.

People think semen is protein-laden because it has the consistency of egg whites. But that's just the temporary action of the clotting proteins. For those, a little goes a LONG way. So don't let the texture fool you. I'm almost willing to bet that cervical mucus has more protein per unit volume than semen

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From "The Straight Dope":

Start by assuming that male ejaculate is roughly equivalent in nutritional composition to raw egg white (a safe assumption). The normal size egg is about 35 cubic centimeters in volume and contains about 14 calories and 3 grams of protein. the normal size ejaculation is about 5 cubic centimeters, or one-seventh the volume of an egg white; figure it, therefore, to contain about one-seventh the nutrients--approximately 2 calories and .1 gram of protein. Of course, you'll have to adjust those figures if you're talking about Jumbo Size (eggs, that is).

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From Weblog:

Here are some facts you should know:

the average guy produces about 3.5 mL of semen per ejaculation whose nutritional value is:
less than 1 calorie
150 mg. protein
11 mg. carbohydrates
6 mg. fat.
3 mg. cholesterol
7 S RDA potassium
3 S RDA copper
3 S RDA zinc
300 million spermatozoa

semen also contains:
water
ascorbic acid (vitamin C)
blood-group antigens
calcium (yes, just like milk!)
chlorine (add your own little contribution to cleanliness!)
cholesterol (Is this the "bad cholesterol" or "good cholesterol"?)
citric acid, creatine, deoxyribonucleic acid, fructose, glutathione, hyaluronidase, inositol, lactic acid, magnesium, nitrogen, phosphorus and potassium (what do you know, these are good for fertilization too!)
prostaglandins (fatty acids that, while not a hormone, perform hormone-like functions)
purine, pyrimidine, pyruvic acid
sodium (good to have, especially if you've been sweating a lot)
sorbitol, spermidine, spermine
vitamin B12 and zinc (you would think it's a multivitamin)

Random fun facts

Average volume of semen per ejaculation: 1-2 teaspoons
Average number of times a man will ejaculate in his lifetime: 7,200
Average total amount of lifetime ejaculate: 18 quarts
Average speed of ejaculation: 28 miles per hour
Its muscle drives nature's only known rotary-joint. The tail SCREWS, not whips. (no pun)
Average number of calories in a teaspoon of semen: 7
Average duration of orgasm: 4 seconds
Average number of sperm cells in the ejaculate of a healthy man: 200 to 600 million
Distance sperm travels to fertilize an egg: 3-4 inches
Sperm lifespan: 2.5 months from development to ejaculation

Now don't you feel enlightened to the wondrous thing known as semen? It really does a body good!