The poll is somewhat unclear.

I think the greatest threat to MODERN society is Peak Oil (or Nuclear War), but global warming is a greater threat to humankind (and all species on Earth)

we need a poll to bet on where rita makes landfall and what category and at what speed
You can bet on where hurricanes will make landfall, and make (or lose) real money at it, at the University of Miami's Hurricane Futures Market. Surprisingly, the market shows a 20% chance of Rita hitting east of Baton Rouge, LA. This suggests an expectation of further northward/eastward movement.
I think that the world situation with avian flu is analogous to New Orleans' situation with hurricanes pre-Katrina.  We all know that we are overdue for a significant event, and features of our current society now make us more vulnerable than before (we are much more mobile now than in 1918.)
A virulent avian flu with a high mortality rate probably trumps Peak Oil or global warming. The abrupt removal of 5% of the population would definitely qualify as "demand destruction".