I vaguely remember around the time of 10.0 that OS X was to be the "OS for the next decade".
That seemed a long time back then. But assuming that statement holds, OS X has just passed middle-age (calendar-wise), and is about to enter middle-age (version-number wise).
The strange thing is, I can't really begin to imagine what might differentiate an OS XI from an OS 10.9. What will be the big technological leap? OS X is arguably already high up the operating system technical tree, which is something that in no way could have been said about OS9 circa 2000. There's no 'must-have' technological trends that OS X isn't already riding.
I suppose that's pretty exciting in and of itself. Finally getting pre-emptive multitasking and all the other shiny tech in OS X after OS9 and below was fantastic, albeit predictable. I wonder what we'll be surprised with in 4 or 5 years?
(sorry... rambled a bit there... what I meant to say was: it'll stay 'Leopard' 😉)