Sorry to perhaps burst your bubble, MissJane...but I somehow think there is no such thing as an "Unplanned" appearance by royals...yes, it was not on their official calendar, yes, the swim people were surprised, but maybe this has been marked in M&F's yearly planner/diary for months in advance...we just don't know how crammed with stuff their daily lives are, little things that we deem trivial, like "wardrobe planning meeting for Beijing Olympic Trip"...but there is probably time allocated for everything in their lives...
What I am trying to say, not very succinctly, is that I feel there is no room for spontanteity in the lives of Mary and Fred...their time is blocked out to the minutes...even mealtimes, etc...but credit to them that they do it in such a way to make it "appear" spontanteous...