Thank you for the warning...I suppose if I wanted to make "vanilla infused vodka", I'd take the vanilla beans out after a few days.
I have vanilla beans that I forgot about in the back of my pantry. They're bone dry, but it seems that this would be a perfect use for them.
I would probably go with a larger quantity of vanilla beans, for a much shorter time -- maybe a week or two (?). For infused vodka, it seems you would want to get the vanilla flavor in there quickly.