One of my wife's favorite songs is Pontoon by Little Big Town. So she picked up last night watching the Country Music Awards that "motor boating" has a meaning other than the obvious. Sure enough (and thanks to the internet) I find that it does. Basically one puts one face between a nice couple of fun bags (pontoons?) and makes slobbery, loose-lip, motor boat sounds. I've done this occasionally in complete ignorance of the name. See
http://vimeo.com/32558339, (a perfectly G rated video) to sort of see it done. Now, all we need are some videos or pics of this particular activity which are more appropriate to our mature tastes.
(I've done this with my face between the ass cheeks, too. But for all I know, that has a different name.)