What fees are associated with the complimentary vacation?

You will be getting the hotel room for free.  However, there is still a nominal activation/tax fee that needs to be paid per night stay.  It is on average $20 USD per night. It may vary according to the destination. 
For example, if you received a certificate to Orlando valued at $785 USD for 4 days / 3 nights, the activation fee would be $20.10 USD per night. It would cost you $60.30 to activate your certificate and get access to the hotel search inventory booking process.

Activation Fee (to be paid prior to accessing the Hotel Search Inventory): Your cost to redeem this incentive and book the reservation is just the recovery fees for the local government taxes and tourism fees which vary by destination. Activation fees average around $20 per night.

Resort Fee (to be paid at your destination): Resort fees, if applicable, cover items like WiFi Internet Access, Local Calls. Resort amenities, Fitness centers, in-room safes, Beach Chairs, Umbrellas, Beach/Pool Towels, activities and more. Resort fees vary by location and range from $5-$38 per night.