(Think about it: 64 bits is enough to give every square millimeter of
earth surface an address.)
Then think that is not that long ago the address efficiency usage was
around 4% (I might remember this incorrect but I have a vague feeling
we where around that at pre-CIDR). I think that the last figure I saw
was at around 35-40%. It's still not that impressive, but also very
hard to get much better (Without research in the field I would assume
that 60% would be close to a practical/theoretical maximum limit (is
there any research done in this field?).