I highly recommend "The Lazy DM" by "Sly Flourish" (Michael Shea) [0] to give you a better idea of how this can be done with almost no effort. I used to be the kind of DM that quantified everything about my world. And indeed, before the internet, it was an excellent time-killer, and seeds many of my modern-day adventures. But I ain't got time for that, now. And so I follow a pattern much like that suggested in The Lazy DM, using index cards. It actually works out really well, since I've discovered that I am pretty creative on-the-fly.

[0] http://slyflourish.com/lazydm/