Port Valet is up and running, use it last Sunday May 26, disembarking NCL Encore in Seattle. They left forms and instructions in the cabin on 3rd day of cruise. Filled out the paperwork and drop off at guest services. Received tags and airlines boarding passes a day before disembarking, attached tags to luggage as instructed, left luggage outside cabin around 8pm, next time I saw our luggage was at our home airport.
Keep in mind that is only available to flights departing SEATAC after 11am. Luggage fee may apply as per airline, unless exempted (I use delta skymiles card so, luggage was free)