Not quite up to your discretion when you use them. I know at least 1 department capped it at 2 days and was told anything over those 2 days were lost(so working through the furloughs with no pay if you had 2 days built up already). But the wording they used basically said that you were giving up the pay already, it was a 10% paycut without having to actually say it is just a paycut.
That would just be loss of pay per employee per month. Would probably amount to only a 1% change for the company since it only affects base pay. Bonuses aren't affected by it, so smaller effect on the largest pays because they are bonus based. They didn't want the vacation days used to cover them because if you can't use enough of your holidays they are gone anyways, so why pay you out for them?