I'm also quite fond of the "forced shutdown days" idea. Shutdown the entire place the week of Christmas and the 4th of July (or whatever holidays, except a skeleton crew to handle emergencies and compensate them with time elsewhere) on top of giving out 15-20 days of discretionary time. That way everyone gets a guilt-free break twice a year and you don't have a hundred thousand emails to come back to.
This is de facto like what the week around Christmas is at many companies. No one expects any work to get done, no one schedules meetings, and no one really audits vacation days being taken either.
