We just arrived home on Friday, November 14. We spent our last day at Downtown Disney and had a flight that departed Orlando at 4:50 p.m. From downtown Disney, it took us approximately 20-25 minutes (at the most) to get to the airport. We left Downtown Disney around 3:00 p.m., had no problems with traffic, checked our luggage at the curb, returned our rental car very easily and quickly (rented from National) and were quickly inside the airport. Inside, things were a little more hectic as the lines getting through security appeared VERY long. However, the line actually split into 4 different lines so it only took us about 10-15 minutes to get through. Then, you had to go board the shuttle or tram (or whatever they call it at the Orlando airport) to take you to the gate area. Luckily, our gate was very close to the shuttle exit.
Although our trip to the airport went off w/out a hitch, I would definitely plan in a little extra time in case you hit a problem. Also, remember that the airlines start boarding (or at least US Airways does) about 30 minutes before the flight is scheduled to depart. (US Airways is the most timely airlines I have flown in a long time. We were always pulling away from the gate several minutes before the scheduled departure time).
Hope this information helps and have a MAGICAL vacation!