Judging by my own experience plus the number of anecdotes in this thread I wouldn't be surprised if it is done routinely. It even makes sense to upgrade couples ahead of single pax in some cases - if upgrading from WTP to the middle seats in CW, for example.
My own experience may be colored by the fact that I'm GGL and both my wife and daughter are Gold, but we've had several whole-family op-ups CW->F. It's an incentive to make sure we're on the same booking - last time we flew long haul together the kid was on a separate booking due to having flown unaccompanied on the outbound, so only my wife and I got the op-up. (I did the decent thing and gave up my F seat so they could sit together.)
Last edited by JonV; Feb 6, 2015 at 4:40 am