Interesting discussion.
Personally, having been raised in a liberal, secular household, I don't believe in waiting for marriage to have sex. Whether or not Clark and Lois decide to have sex before they're married doesn't matter to me as long as their decision is explained in a way that makes sense to me.
On the show, I had the feeling they just glossed over it. We had Clark confessing to Lois that he was a "very patient man" and then--bam!--we have them in the newsroom, talking about hardly being able to wait for their wedding night, and fade to black.
How did they get there? Now that the subject was out in the open, and the physical aspect of their relationship had been discussed, why did they decide that they were going to wait?