Our last stay at the Dolphin was $139/night, INCLUDING taxes and resort fee, which is a great deal. We booked through Travelocity. I'm an RN and the rate through Travelocity was better than the nurse/teacher rate (which does not include taxes or resort fees).
We are going again in 10 days and again booked through Travelocity, although this time we are paying $496.44 for 3 nights including taxes and fees--not as great a deal as last time. But we could only have gotten the nurse/teacher rate for 2 of the 3 nights, so it still worked out better to book through Travelocity.
Be sure to check all the major sites (Travelocity, Orbitz, Hotelkingdom, etc.) as well as
Dreams Unlimited (on the home page of the DISboards), Mousesavers.com, and the Starwood site (corporate owners of the Dolphin).
I, too, saw the $100/night rates mentioned on the boards about a month ago--they were for a very limited time frame. If you are flexible on dates, keep checking all the sites, and be sure to post on some of the Dolphin/Swan threads that you are looking for low rates.