like timmay i haven't bothered to read most of the posts, but....
from someone who's made mistakes about the way people have felt about me in past relationships, i think its best to hold off sex until you know the kinda person you are, the kinda person your partner is and the way your relationship works. for some, this will mean not having sex until marriage, because that wait should be sufficient to work all of those things out.
that being said, i dont think that having sex before marriage is a big thing- my friend's brother only married his girlfriend because he had sex with her and then thought he should marry her because the Bible says, basically, that you should only have sex with the person you'll marry. 4 months and a divorce later, he found out it was a bad choice.
if you're a christian and you want to wait until marriage, good on you- that way you're sure not to get hurt or have shit experiences with dickhead boyfriends and the like.
then again, the Bible is not 110% contemporary, and you cant say someone who has sex outside marriage is not a christian. it depends on your evaluation of things, what kind of person you're dating and your way of looking at the relationship.