What kind of bikes are important? The cheap, indestructible, heavy bikes that are ubiquitous in the third world? Or the zippy, expensive, modern bikes that you find in American bike stores?
James on the Bike Design blog acknowledges that the work horses provide vital transportation to people who can't afford other means. But, he argues that bikes that people buy out of necessity are not going to solve the more pressing problem of getting people who can afford cars to choose bikes instead. (Even in underdeveloped countries, bikes are seen as symbols of poverty.)
Is there a bike (or bikes) out there that will help convince people to use their cars less?
Maybe it's not the bike, it's the infrastructure. Is there a type of bicycle accommodation that will get more people riding?
I suspect it's more an infrastructure issue. There are plenty of developed countries with robust bike cultures, but where's there is widespread bike usage, there is typically a biking infrastructure and culture. Anne sent a link to this speech by the Mayor of Munster, Germany, detailing all of the steps he took to transform his city into the most livable city in the world. (Here's the presentation that goes with the speech.)