Lots of times---ITA with the Geyser Gazer: 5 hours door to door, with one quick stop for gas. Haven't gotten a ticket yet, so while we go fast, we aren't crazy. Watch out in GA, I think they are balancing their state budget on speeding tickets.
Another tip: leave early in the morning. Less traffic, better time, and you arrive at WDW in time to do a half day at the parks. This tip is imperative if you make the drive during the summer months, especially on a Saturday.
I agree with Mapquest. They've obviously figured in my stops at the Beltz Outlets in St Augustine, my stop st the Florida Welcome Center, stop for breakfast or lunch and gas.
Seriously, over 30 trips, with no traffic we've done under 5 hours and with bad traffic and construction almost 7 hours.