So how should they fit? I was told directly (in person) by a Vibram Five Fingers corporate rep to fit the toes just BEHIND THE TOE CAPS or right in that area—obviously with different toe lengths there is going to be some fudging here! That means there is a decent amount of room between the toes and the end (close to 1/2″) and there may be some bagginess in places depending on your foot volume. Keep in mind that your foot will swell while you are running so any snugness you feel in the store should be a red flag.
Of course this tip is only useful if you can find a shop that sells Vibrams before you shell out your cash or you have them in your hand. That said, my less-hands-on approach seems to have resulted in a similar fit as that suggested here.