2001: A Space Odyssey
I had not thought of this example, and I just now saw it and grasped for the first time why having colons in titles is a good thing.
I now side with Lee -- we should allow colons in titles, software wise, but have a "simple convention" as he puts it to avoid them whenever possible. But there are cases -- movie titles, book titles, and the like -- where they are indispensible.
If a few articles have titles that conflict with some future desired namespace, we can easily fix those few at that time.
--Jimbo