I've been growing my own sourdough culture for about a month now. I started by culturing some storebought yeast, and have kept it alive in the back of the fridge since then. Yes, culture storebought instead of using captured wild yeast is both cheating, and leads to a less interesting bread. It's about 20 degrees outside now - once it gets over 65, I'm going to start a new one with outdoor wild yeast. Starting one indoors during the winter just seemed like fermenting dust bunnies, and that's just not something I want to eat.
About 1-2 a week, you need to feed and bake, or pour some down the drain, so the upshot is that I've been baking more, and getting my techniques refined. Using the starter gives a fuller flavor and nicer color to the bread than instant yeast - give it a try sometime. Here's a nice writeup on how to get started--->LINK