Another interesting factoid I read somewhere today: on average only 15% are fit enough to even reach the egg. Yet sperm fitness has been measured to increase after exposure to pornography involving men and women, while this effect is apparently not observed after viewing lesbian pornography. The theory is that seeing the competition somehow makes the sperm more competitive. And that's why it's better to hang around with your fellow HN'ers than your nay-saying friends.
There are approximately 200 to 500 million spermatozoa per ejaculation: http://en.wikipedia.org/wiki/Semen and a man produces 50 - 300 million sperm/day. I'll let this guy do the math: http://members.shaw.ca/tfrisen/chances_of_you_existing.htm