Here is a 3 minute video that answers that question. Please forgive the fact that a lot of it is a pitch, but the content is strong. WE HAVE NOT RESEARCHED THE COMPANY THAT PUT IT OUT, so please do not take posting this video as a plug for them. The information is good.
What are your thoughts on it? Is it the next big thing or a fad in the wind? Ford seems to think it will work — they just put one out recently about their 2008 Focus.