Shiv,
I have an 11 and 13 yr old daughter, so trust me, wherever you are, I've both been there and am still currently there. And if there is one thing I've learned over the years is that kids are far more perceptive and up to speed on things than we think. And kids can certainly be far more analytical that we give them credit.
As it pertains to "Adult issues" I think the whole "taboo/never talk about it/ pretend it doesn't exist" thing leads to more problems than it prevents. As kids become aware of things, parents discussing it with them in an open manner takes away all the mystery of it and all the "ohh, ahh, its soooo bad" aspect of it.
How hard is it to say, "yes some people choose to do it, but it really screws them up emotionally, physically, etc and its really not a great thing to try out or aspire to". Its when you try to hide it and sheild it that it only gets kids curiousity up and turns it from a molehill into a mountain and they seek out info from undesireable sources. I'm not saying you should show porn to your kids, but having frank discussion about people who choose that lifestyle, and being open and honest about how destructive it is helps them develop more informed opinions of it as opposed to turning the other way, pretending it doesn't exist, and only adding more fuel to thier inquisitive fires.
My $.02