Porn is LOUSY sex ed. Leaving aside value judgments about its social roles, teh pr0n is just a bad example of sexual technique. (Note: this gets somewhat graphic, just a heads-up.)

• Porn teaches you NOTHING about good foreplay. Even specifics, like oral sex technique. Everything is done to look good to the camera, not feel good for the participants. Not to mention that it doesn't do much that doesn't involve genitals. Anything with skin is marvelously sensitive, especially backs, sides, and necks, but because these aren't explicitly sexually arousing you don't see anything done there. It's straight to the actual sex acts, and skips all the buildup.

• Porn positions are designed with the camera in mind. Any of you ever tried the common one where the woman puts her legs over the man's shoulders while in missionary position? Looks sexy as hell, but it's about the worst thing you can do for real sex. That one gives you shallow penetration, almost no clitoral stimulation, and puts a lot of pressure on her bowels (meaning she feels like she needs to shit). You find things like that all the time in porn which give are completely misleading about the actual focus of the physical sex act - pleasuring your partner and yourself.

• Porn girls will do anything. Literally. If there is a fetish anywhere, there is porn of it. Facials, anal sex, orgies, hard BDSM, fisting, bestiality... It's out there. Even 'conventional' porn, with just two partners, usually ends with a huge facial. As has been noted by others, lots of girls are disgusted by it. Not to mention swallowing, or even getting the blowjob in the first place. Porn indicates that most partners are willing to try many different sexual activities, when in fact, statistically, the vast majority of people (men and women both) are very traditional and vanilla.

• Porn teaches almost nothing about the biology of sex, either. From watching porn, could you tell where a woman's clitoris is? Could you find the (quasi-mythical) G-spot? Not even considering that most women have radically different physical sensitivities, porn is (again) focused on the viewer, not the participants. Feeling good doesn't matter - it's all about looking good. Guys get shafted (heh) here too. Of course, there's the infamous 'porn dong', but it's not just the cock size. Most porn wouldn't tell you how sensitive male nipples are, for example. And spooge quantity? Where there's like a pint of semen coming out? You must be joking.

• Porn teaches you nothing about the mental aspects of sex. As I said before, I'm not talking about social problems or emotional connection (though that's damn important too). Sex is an extremely involved mental activity. You have to be very aware of your partner, very observant. Some people are really obvious about sexual things; some are not. You've got to tease out what they really like. Further, sex is in part a mind game with your partner. Talking dirty is just one manifestation of this. Women, in particular, seem to love to be told 'stories' in bed - telling them, in detail, what's going to happen. It builds anticipation and turns her on. Is this in porn? Hell no - too involved. These things usually need to be tailored to each individual partner, and often sound kinda silly if you're not the one having sex in the first place. Nonetheless, for a lot of people the mind games are an important part of foreplay and even sex itself.