I'm not surprised by the statistic on sexless marriages. Sex is something that's very intimate, exposed, makes you vulnerable. If you've fallen out of love with each other or have lost trust in each other, sex would be quite uncomfortable, to say the least.
We do it whenever we can (read: whenever the baby is sleeping and we're both awake!) Not that you guys want to know this or anything, but we just had a quicky on the sofa - 4pm. We take it when we can get it. Anywhere from 2-5 times a week, I guess.