Depends alot on where you live though. Here in Minnesota at least, the owning just a bike thing isn't in the slightest a viable option. Maybe someplace with less tempermental weather you could pull it off. Point is that if its storming like mad and you need to get somwhere, ie. work, hospital, gas station for smokes, whatever, owning a bike won't do you any good. I'd rather not curtail my entire life every time the weather goes bad.
And where I'm living now (moved out of Mlps), no cabs, no buses, no enterprise. I'd say it really depends on where you live and how much of you life your willing to let the weather rule. Persoanlly I just couldn't imagine not having a car. I'm getting a lil older though, your tolerance for things changes as you age.