Clarke wrote 100s of books and as others have said contributed to and encouraged much scientific development. He was an advocate of developing technology to explore and (eventually) colonise other worlds. Nasa in particular benefited from his influence and many there considered him a friend. The scuba diving is true and some of the astronauts used to join him. It seems they all get training in scuba diving to simulate weightlessness and many find they they enjoy it.
When he was about to be knighted the papers needed something to say about him so as usual they invented stuff. This would be harmless were it not for people who say "oh well I read it in the Daily Mail/Express/Beano so it must be true"
I remember him saying that the way the world was going your best bet if you had the option was to move to some out of the way place that no one would want to invade/bomb. The way things turned out Sri Lanka probably wasn't the perfect choice, but where is?
I will miss his writing and I'm sure that all who knew him will miss the man.