Sasha,
With all due respect to Rick, having lived in the Luberon now for 13 years, I can assure you that "terminally quiet" is a bit of an exaggeration ! For example, of all our favorite restaurants in the area, I can think of one which is shut for vacation that time of year. Likewise, the vineyards are all open for tasting and actually kind of happy to do so as the harvest will be all finished by then. As a bonus, there are quite a good number of fall/harvest village fairs and festivals going on in various places and various weekends. In October, they are generally focused on either wine or "fall" produce (there is an excellent mushroom festival for example which comes to mind).
As for tourists running around, there are certainly less of them than in the heat of the high season. That's actually probably a good thing for you.
And lastly, it'll start just after you leave, but the French schools have a 2 week mid-term break (for the Toussaints holidays) - so things end October and November can get more crowded, though once again nothing like the summer.
