it's $25 per night and added to bookings made before the fee was in place. Was able to book the Aloft for significantly less for the same stay so cancelled the Westin since I'm in for 3 nights. Contemplating the Marriott down the street for $165 (inclusive, post paid) a night.
I've stayed at the Westin enough to know I won't get additional value for the new fee regardless of what it provides.