When I travelled in the UK, folders were fairly common. While still vastly outnumbered by "normal" bikes, I saw folders in London numerous times every day. Part of the reason is that many people don't own cars. Cyclists often ride their bikes to and from the public tranist stop and fold them while on the bus or train. I saw all kinds of people on folders, including business types in three piece suits. There are at least a couple of magazines that cater largely to folder riders (A to B and Velo Vision) and there is a "Folder Society" as well.

Re: the USA. Even the major oil crisis that I'm old enough to remember didn't shake us out of our cars and onto public transit, so that part of the equation probably doesn't add up to much. And at big events like Bike Virginia, a folder is much, much more of a novelty (if that's the right word) than, say, a recumbent. However, I do think folders are beginning to make a small dent. I spoke with a rep from Bike Friday yesterday. He said last year was one of their best ever, and they are expecting strong sales this year as well. Having said that, my understanding is that something like 12 million bikes are sold in the USA every year (most of them dept. store cheapies). Out of that number, I'm told Bike Friday's sales are probably in the low thousands. It would be interesting to know Dahon's numbers.