I have participated in various incarnations of this race for the last 3 years and will be on a team this year. (This will be year 5) It is great fun!!! The folks that organize it are Florida locals and have extensive knowledge of the parks.
The first couple of years the race was run, it was a pure scavenger hunt with about 500 extremely obscure questions. Last year was the first time they tried the Amazing Race format and it was also a lot of fun. The more teams that sign up, the better the race (and prizes) will be!!
It does take ALL day and you must be prepared to use a day off of your park hopper (or AP) with the possibility of not riding a single attraction. But then again, you may ride many attractions. You will visit parts of the WDW resort that you may have never been to before and you will spend a lot of time on Disney Transport. You will also walk a LOT more than you normally would in a park day. One of the racers usually has a pedometer with her and has averaged about 14 miles walking each year she has done the race/hunt.
Hope to see you at the race!!
Carol (1/2 of the Mission: Race!! Team)