I agree, I think the two crucial elements must surely be: i) the woman being comfortable with the partner - there must be plenty of guys who would freak out thereby causing inhibition in the future, and ii) the guy (or partner to be more balanced, they could just as easily be female) needs to be sensible and sensitive enough to locate the correct area.

Like riding a bike though, once you get the knack it seems to follow very naturally. I make sure to tell my SO just how much I like it, how much it turns me on and how close to her I feel because we can do this. Personally, we find that gently massaging her bottom (using aromatic massage oils) as part of the foreplay and during the stimulation, adds an extra level of "oomph" to the proceedings.