Which means that, at the reference difficulty level, it can be expected to happen every 10,000 blocks * 10 min/block = 100,000 minutes.
That is, once in 70 days - or 10 weeks.
Definitely not a once in a lifetime event, if Philip's numbers are correct.
Once in 10k days, not blocks.
Good of you to set me straight, @suchmoon.
Hm, so Philip's numbers were correct, but apparently my lucidity was a bit off.
I should really have left the math to the llamas.