The only person I've ever personally seen, that I absolutely know for sure is flying purely for fun and no other reason, is Guppy/CorkyJr. Nobody but nobody seems to enjoy the simple pleasure of upping a virtual plane for no other purpose than to see what kind of trouble he/she can get into.
I'm not saying other folks don't fly like this, but in my experiences nobody exemplifies the 'just play for fun' statement like him.