Brian Hayes had an interesting column last year on what could happen if these became common, or even universal.[1] One advantage he pointed out was that you wouldn't have to waste time looking for a parking place. The car could drop you off right at the door and then go, maybe far away, to park. Valet parking for everyone!

[1] http://www.americanscientist.org/issues/id.13359,y.2011,no.5...