I did a stout with just one bean for fear of two being overpowering. I did the standard soak in vodka for a couple of days and poured the lot in.
Stout "part" turned out... okay. Drier than I expected, but not bad. No vanilla flavor at all, though. I'm assuming either I did something wrong, or I next time I experiment a little more and do two beans.
I also plan on leaving a liter or so out to stale. I would love to try for a mix of the Guinness "sour" flavor with the vanilla. /dreams