I have a ton to say about this but it's going to have to wait until I have enough time to do it justice; for now, you should read this Pandagon post about "affirmative consent," rape, and the law. It is very good and very important.
If "She never said no, so it can't be rape" is an argument, how is the converse ("She never said yes, so it was rape") not also a valid argument?
I've always argued, and will continue to argue without apologizing, that not all communication needs to be verbal. There are clear and obvious ways to say yes – initiating sexual activity or being receptive to initiation by someone else – and no – pulling back, pushing away, clamming up, etc – without using words. Sexual activity does not and should not require on person saying "WOULD YOU LIKE TO HAVE SEXUAL INTERCOURSE? IF YES, PLEASE SIGN HERE" nor the other saying "I CONSENT TO SEXUAL INTERCOURSE, INCLUDING THREE TO FIVE MINUTES OF MANUAL STIMULATION AND NO MORE THAN FOUR (4) SLAPS ON THE ASS." But to claim that this is the "feminist" argument is to create a Straw Man.
It baffles me that so many men appear to find this concept so difficult. If you are not sure, you have two options: ask ("So…do you want to do it?") or – and this is the one that blows minds – don't have sex. I've heard every hypothetical what-if situation in which the poor male is victimized somehow by the rules of consent and yet I have never heard a single one that could not have been resolved by one of those two options. Not one. Ever. Those two choices that all men have work 100% of the time.