This. I most assuredly will NOT marry a chick I haven't slept with. If we are incompatible in the bedroom, the relationship isn't going to work out, period. Sure, sex on the first date is...well, kinda sleezy. I certainly don't do it. But at SOME point while dating, if the girl says "I'm waiting for marriage" (and this has actually happened to me lol) I will break up with here right there and then unless she changes her mind. I also have a friend of a friend, female, who is 'waiting for marriage' and hasn't been in a relationship longer than a couple of weeks. That lifestyle and belief is so far outdated, nobody wants to put up with it anymore. As asshole-ish as it sounds, put out or get out. That goes for both men AND women, though I can't say I've ever met a man who wanted to be chaste until married...
It's not about getting another notch on your belt, or 'claiming the prize', or anything like that. It's simple relationship chemistry. Like I said, if you aren't compatible in the sack, while relationships certainly should not completely and totally revolve around sex, the relationship is not going to be a very good one. If the sex is bad, one or both parties might start seeking sex elsewhere, which could end the relationship in a really bad way. Nobody wants that.