Fuck NO. Never, not to anyone I'd ever dated. It's completely reprehensible.
Coming from a guy who's been cheated on by every girlfriend he's had, yet still has never cheated, or even lied, to a single one of them... You'd think I would take a chance to after 11 years of bullshit. But every girl I date I hope will be 'the one' and wouldn't risk the possibility of that being true for anything. I've always cared about the relationship after all, not the sex. Although sex is always a good part of the relationship, don't get me wrong!
Anyway, I find sex to be completely pointless if there's no connection with the person you're with... It's got to be more than mere lust, otherwise I won't enjoy it and just get bored and finish off as quick as I can. Where's the fun in that?! I need the emotion, for it to be really intense and enjoyable.