The comments thread has been both heated and interesting. One comment struck me as both understandable and rather horrific. Darsh said "It is true that guys regularily need to press on through token resistance by girls".
This is a pretty commonly expressed opinion, and it both is a problem and reflects a problem. It's a problem because it's impossible for a person to know if what their partner is doing is "token resistance" or reluctance mixed with fear. If it's the latter, consent is clearly in question. If you can't be sure that you have consent, you shouldn't keep going.
However, it's also true that women do put up faux resistance from time to time. It really, seriously shouldn't happen*. It does happen because women are told they can't be sluts, that they need to be coy, that they need to play hard to get. They are taught from a young age not to own their sexuality. So they do, from time to time, play these games.
So what to do? I think there are two parts to the answer - the short term and the long term. In the short term, men (most often, but women too) need to just stop when their partner puts up "token resistance". It's not a fair thing to do, to pretend you don't want sex when you do, but it's understandable given how women are socialised. It's up to us all to change this habit. I'd suggest that sex ending as soon as someone starts playing coy is a great way to do this. If she's doing it because she really doesn't want to be there and is afraid of the consequences of saying no, that's the only ethical option anyway. If she's doing it because of what amounts to fucked up social training, if you can encourage her to express enthusiasm for sex actively - well everyone has a lot more fun.
The longer term solution is to actually put some sex education into sex education. Teach kids that the first step in having sex with someone is talking about sex with them. That everyone should be clearly and happily expressing their desire before anyone pokes anyone with anything. And most importantly, make it really clear that this isn't a policy of prohibition, it's a recipe for good, safe, respectful and FUN sex. If you're gonna do it, do it right.
*Unless it's in the context of well defined and discussed play.