It helps to keep historical analogues in perspective.

Just eyeballing a Thirties production chart, it appears that world oil consumption only fell in one year, in 1930. As "Downsouth" noted, there were three million more cars on the road in 1937 in the US than in 1929. The key difference regarding auto demand between now and 1929 is that hundreds of millions of people worldwide want to drive a car for the first time now versus millions of people in the 1929.

In the early Eighties, we obviously saw a decline in demand, but the price decline was very gradual (price decline of -6%/year from 1981 to 1985), as Saudi Arabia cut back on exports. The big price decline did not occur until Saudi Arabia boosted their production and exports in 1986 (price decline of -73%/year from 1985 to 1986):

And it remains to be seen if the 2009 average annual oil price will be below the 2008 average price.