You can learn a lot from watching porn.  Here are just a few observations that I have made over the years.  These may not be applicable to real life.

1.  Women wear high heels to bed.
2.  Men are never impotent, no matter their age.
3.  When going down on a woman, 10 seconds is more than satisfactory.
4.  If a woman gets caught masturbating by a strange man, she will not scream with embarrassment, but will insist he has sex with her.
5.  Women smile appreciatively when males splat them in the face.
6.  Women enjoy having sex with ugly, middle aged men.
7.  Women moan uncontrollably when giving oral.
8.  Women always have an orgasm at the same time as a man.
9.  A blow job always gets a woman out of a speeding ticket.
10.  All women are loud in bed.
11.  Back in the 1970s, people couldn't have sex without a wild guitar solo in the background.
12.  All breasts are real.
13.  A regular and enjoyable sexual practice is when a man takes his half-erect penis and slaps a woman in the face with it.
14.  When a man has an orgasm, he will always say, "Oh yeah!"
15.  If there are two men having relations with a female, they most certainly always high-five each other and the woman is never offended.
16.  Double penetration makes women smile.
17.  For some reason Asian men do not exist.
18.  If you happen across a couple having sex in the bushes, the male will not tell you to get lost but will insist that his girl's mouth is ready.
19.  There's plot.
20.  Slapping a woman on the butt is always excitable for the woman involved.
21.  Besides giving medicine, nurses give other jobs to male patients.
22.  Men always pull out.
23.  When your girlfriend catches you in bed with her best friend, she won't be angry, but will join you in the festivities.
24.  Headaches do not exist.
25.  When receiving oral pleasure from a woman, men it is pertinent that you remind them to "suck it".
26.  Everything is always clean.
27.  Men ejaculating all over a woman's body is a satisfying result for all parties involved.
28.  Women are always surprised when opening a man's pants to find out that he has a penis.
29.  Men never have to beg.
30.  Pigtails=handlebars.
31.  Hitch-hiking is glamorous and always results in sex.
32.  Pizza delivery boys and repairmen are the greatest jobs a man could wish for.
33.  Pizza delivery boys and repairmen always have sex when they deliver or make house calls.
34.  All food in porn movies is nothing more than another sex toy.

Here are some that were submitted by Xanga users.  I didn't include their names because I didn't know if I had permission to repost them.
35.  Women enjoy getting slapped with penises
36.  All lesbians are “girly”
37.  All lesbians carry bags filled with sex toys
38.  All stockings are crotchless
39.  Baby oil and saliva are acceptable lubricants
40.  All women are hairless
41.  Playing with globs of saliva is sexy

42.  All women are ready to jump in the sack with anyone at anytime.
43.  Big penises make up for lack of personality
44.  Normal penis size is 12” and anything less is unacceptable
45.  Ron Jeremy and John Holmes are somehow sexy and appealing to women
46.  The majority of female porn stars are rail thin, fake tanned, with humongous boobs. 

47.  If there is more than one woman in the scene they will inevitably get it on while the guy enjoys. But if there is more than one guy in a scene they NEVER get it on while the girl enjoys.

48.  Females have an infinite amount of spittle.

If there are any observations that you have, please share.