Math nazi in me really wants to point out that an event with a 1:1000 probability would be expected to be seen (> 50% probability) in about 700 years, not 1000.
Heh, hence why I said 1-in-1000-year, rather than just 1-in-1000. Indeed 1:1000 would happen within 693 years with 50% probability, 1:1443 would happen within 1000 years with 50% probability.