According to a recent survey to be published in the May issue of the Journal of Sexual Medicine, good sex (not including foreplay) takes
3 to 13 minutes
Please tell us what you guessed before you looked at the spoiler or clicked the link. It might also be interesting if you indicated your sex.
Bumping nasties in the AM before work: 3 min
The long bath shoulder rub foreplay oral sexathon: 30 min - 1 hour
Both are very different, both good.
Male-
At least 45 minutes or so.
I’d already heard of the study so I knew the ‘answer,’ but that highlighted bit makes the findings pretty irrelevant, IME. That’s like asking ‘How long does it take to eat a good meal? (minus appetizers and dessert)?’
If we’re just talking the act of coitus, from first penetration to male orgasm*, I’d say four or five minutes.
20 minutes to over an hour depending on how energetic I and the wife feel at the time. Both of us usually have multiple orgasms (her more than myself, of course). But then quickies can last less than 10 minutes and are still good, too. Damn, most all sex is good when you cum to think about it.
Depends on if it’s with the wife or the girlfriend.
This thread is right next to “Choosing a new personal device.”
A lifetime. And I mean that in a good way. 
Seriously, maybe I’m odd, but I say 20 minutes, minimum. That’s for fast, hard, crazy sex.
Slow, gentle, take-your-time-and-enjoy-it sex takes at least 45 minutes.
I’ve had the 5-10 minute sex when we’re in a hurry, and it gets the job done… but it’s like a McDonald’s hamburger when you really want a steak. Satisfies the physical urge but doesn’t really cut it mentally.
All this is penetration to orgasm. Tack on a few more minutes on either side for… well, just use your imagination.
Before I clicked the link I couldn’t guess because all I have to go on is my own experience.
Before my last partner, I’d have said probably around half an hour or so. Afterwards, I’d prefer the really intense kind (with most all the goodies packed in) to at least last 90 minutes. But for a quickie, well all bets are off. Those can be pretty hot no matter what the duration.
… Especially if your pushed up against a wall in a semi-public place. I’ll be in my bunk with my headphones on.
Quickies can be great, but so can fucking all weekend. The best sex I ever had was when a friend of mine who I’d had cyberfling with online came to visit. We basically had sex for the three days she was there, with obvious breaks but sometimes we went for hours at a time.
It depends on how much she charges per hour, and whether or not she prorates it.
Maybe I’m just weird, but limiting the timing to the penetrative part of sex strikes me as weird. Actually I can pretty much take it or leave it when it comes (heh) to penetration. Sometimes we’ll finish up with penetration (in which case 3 minutes is sometimes rather optimistic, depending on what she’s been doing to me beforehand!) but often not.
I find my orgasm is usually more pleasurable when it’s not constrained by being inside a vagina. (Now how clinical does that sound?)
Yep, maybe I am just weird.
Depends who you ask, me or my girlfriend 
I’ll go with 3-4 minutes, how long I think I last.
On uncovering the spoiler, I just make it
Yeeeeah… um. An egg timer would do.
It shows up when you hover over the link.
Long enough to reach the ground.
Personally, I can be quite satisfied after five minutes.
She’s multi-orgasmic though so we usually go for about 20 before I get to finish. I’m caring like that.
So much for spoilers, eh? I never noticed that.