In the second book…isn't there a scene where Elend and Vin (and Spook) run away from the city and they're in their tent, and Vin is top-less (at least) and they kiss and stuff and Elend wants to do something else but Vin doesn't…I don't know something like that.
Yes, there is, and since you mentioned it, I just read that part over again, and it is strewn with sexual innuendos. No, it doesn't come right out and say anything blatantly, but it's exactly like Natalie said--reading between the lines, it's there. And in that particular section, you don't even have to read very much between the lines, because....well. It's obvious enough.
I mean, here's a few quotes:
Elend Venture awoke on the third day out of Luthadel, surprised at how rested he could feel after a night spent in a tent out in the wilderness. Of course, part of that might have been the company.
Well of Ascension, pg 629 (US Paperback)
Then later, when Vin wakes up.
"You're a bad influence on me."
"Oh?" he asked, smiling as he rested on one arm.
Vin nodded, running a hand through her hair. "You're making me get used to sleeping at night," she said. "Plus, I don't sleep in my clothing anymore."
"If you did, it would make things a little awkward."
Well of Ascension, pg 630 (US Paperback)
And then, after that there's the part Shaggy's referring to, where Elend tries to pull her down after she's dressed and is about to leave the tent.....
I've already said it, but I personally think that the sexuality that is currently in the books is a perfect amount. It's there, but it's just enough that it doesn't detract from the plot, and that's good. Plot-detracting sexuality isn't that kind of sexuality that I care to read about...