The mile-high club is due for an upgrade--every planet has its luxury limits. NASA has distanced itself from the rumblings and rumors of sex in space, but that hasn't stopped the dialogue from happening.
Richard Branson's Virgin sub-orbital space tourism venture is at the head of the pack, although they're quick to admit that there are considerable challenges. On Earth, gravity keeps moving mass in check, making it easy to change direction quickly. In a zero-gravity atmosphere, objects put into motion continue to move until they bump into something. This is particularly problematic, for males in particular.
Proposed solutions to this issue include handles, bungees and straps. There is even a 2suit concept sleeping bag-style spacesuit for couples to zip into. Some researchers aren't as concerned with the logistics as with the potential consequences of sex in space.