I have 4 sons, so we're in different worlds to some degree.  I agree about the open and honest conversations.  As my boys (the older ones are 10) have gotten to the point of even being able to tolerate the subject we've brought it up.  

Because I'm with them so much of the day, I usually am the one doing the talking, but so far that's been okay.  Their dad gives input if it comes up when he's at home and I anticipate more father/son talks in the future as conversations become more....detailed.

Two concepts that are bedrock to my parenting are foundation-building and arming.  Everything I do-everything-with the boys is about laying a foundation for the future.  They get irritated with me for making them learn different things, but I want them to have as much experience in as many areas as possible by the time they're 18.  I've considered adopting Monk's line: "you'll thank me later."  Lol.  

As for the arming, that's a biggie too.  I try to explain to the boys in advance what will happen to their bodies over time and how that will affect their thinking and feelings.  (Right now they still think girls are gross.)  When the change does happen and girls start looking attractive, hopefully they'll think "Hey, mom and dad told us this was coming" and trust us more.  I also plan to be pretty detailed as to the possible costs of pre-or extra-marital sex in hopes of strengthening their own discipline.

Of course if they don't make it to marriage as virgins, we'll deal with it.  It's not going to make me stop loving them.  I'd probably sigh a bit and roll my eyes though.   I have a friend whose nephew got a girl pregnant and wanted to be a father to the child.  The family was heartbroken when the girl wouldn't allow him any kind of rights and it was a big mess.  I didn't hear how it came out, but that was an unexpected scenario.  I hope it's not one that plays out for us.