I think the trick to Mass Transport is that it has to make more sense to use than driving. If it's cheaper, and easier to drive from one point to another and is at least as "Sane", than the Mass Transportation is not up to snuff.
I'm talking day to day, by the way, not into the City for a big event. Though, there's that as well.. if it, for example, made more sense for me to drive to RFK stadium to see the Nationals (and they aren't far away) why is it worth it for me to take the Metro?