The thread seems about answered and I can't add much to the answers previously given. But, just to reinforce, my girlfriend and I actively pursue being pure with each other, and we cuddle together on beds, but mostly carpeted floors or a couch or somewhere a little more public (friends, family, etc.) so that people don't have any misinterpretations. We enjoy being close physically just as we enjoy being close intellectually and emotionally and spiritually.
With that said, we don't have sleep overs. When it gets late we can't trust our minds anymore. When we are tired, we are attacked by ideas we conquered long ago. So just for the sake of safety staying up late together just isn't a good idea, and is something my relationship focuses on and we try to encourage not staying up together.
Secondly, sleeping over just isn't a good idea due to what people may think. If you want to be an image of who Christ is why would you want to taint someone's image of who you are as a Christian, even if you arent
sleeping together how does anyone else know that. This is along the same lines of getting under a blanket together. One's mind can wander what is going on underneath of that blanket. Plus Scripture say that while we are free through Christ we should limit our own freedom so that we can save others. And how can we do that if we look like a hypocrite - in someone's eyes - preaching to not sleep together before marriage while we go and "sleep" together. While it is definitely hard not to look like a hypocrite as a Christian - or as a human being for that matter - we should take steps to allow for a more positive outlook on ourselves and Christ.
Along the same lines, we should not be stumbling blocks to our Brothers in Christ. That maybe cuddling is something that is a stumbling block for somebody. So doing this in private (private as in somewhere that wouldn't give off a negative outlook from someone and also somewhere that wouldn't allow for stumbling of our Brothers in Christ), may be the best. For example, if your roommate cannot cuddle because it leads him to more than cuddle, then cuddling on the couch in the living room may not be the best place to cuddle, while cuddling in your room may be to private of a place.
A lot of thought and thinking goes into a simple act of intimacy but that is what I feel we are called to do as Christians is too think. Maybe I have thought too much and maybe I haven't but take what you want from this and leave what you don't. This has actually helped me a lot just too realize what is appropriate and what isn't in my own relationship.