"What do you think about sex?"
Feels good man.
In all seriousness, I think as long as it there is form of protection being used and it's between consenting adults, it's all well and good.
I personally would not like to have sex with someone I'm not in a relationship with - but that's more due to the fact that I'm a tad self conscious and I'd like to know the person well enough to trust them not to stare/mock/laugh or whatever.
But I don't dissaprove of or look down on people who have sex outside of a relationship. Each to their own and all that jazz, and not really any of my business IMHO.