I've made it through one full bottle of homemade vanilla extract. Now that it's been about a year and a half, I can tell you it's been totally worth the work, cheaper, and better tasting real store bought vanilla extract. You can see how I made my own vanilla extract, and how it it was after about 8 weeks of waiting.
I guess I haven't technically consumed the last 4 ounces, since I just decanted it into my small bottle that I use for easy pouring for cooking/baking, and I gave away about 2 ounces to my mom. I do know that all the vodka that was in the bottle I used to replenish the first batch is all gone. Replenishing the bottle as I used it has worked really well for me. I just decant 4 ounces of the finished product into the little bottle, and add new vodka to the vanilla bean bottle. Shake it up, and by the time I'm ready to refill my small bottle again, it's been several weeks, and the vanilla is nice, dark, flavorful and wonderfully aromatic.
One interesting thing I've noted with my homemade vanilla is that over time, the liquid has become slightly syrupy in consistency. I don't know if this is good or bad. I'm assuming good.
Now the question for me remains if I should keep replenishing the bottle I have, or if I should just start a brand new batch, and let it sit for a year (while I use up my current batch). At what point will the flavor of the vanilla diminish? When will the usefulness of these bean pods be exhausted? I suppose I could run an experiment - I could keep replenishing the vanilla bottle I have, and start a new batch. I'll be set with vanilla forever!