I brewed a vanilla porter and used 1 whole bean. I chopped it up, seeds and all, and put about an ounce of vodka over it. I let it soak for a week like this, then added the tincture to the primary after fermentation was winding down. I left it for 7 days in the primary. I got a lot of vanilla flavor. I think the vodka extracts every last drop of flavor from the bean and serves to sanitize it as well.
We brew a vanilla amber ale where we drop 1 sliced open vanilla bean into secondary for about a week. It gives the beer a lot of vanilla flavor which is what we were looking for with this beer. We are also going to add 1/3 of a bean to our Coffee Porter to round out the tannins a little bit. I love using vanilla beans but just be careful they can impart a lot of flavor in a short amount of time.