We made our first drive down to WDW (from Connecticut) in mid-February. We left on a Friday night (around 9:30/10:00) and drove to the in-laws house in New Jersey. We spent the night in NJ and left the next morning around 10:30/11:00. On Saturday, we drove as far as Harrisburg, Nouth Carolina where we spent the night at my brother-in-law's house (we arrived in NC around 8:30/9:00). We hung out in Nouth Carolina on Sunday and on Monday morning (around 6:00 or so) we left for Florida. If memory serves, we hit the "Welcome to Florida" sign around 3:00 p.m. and it might've been 4:30/5:00 before we arrived in Kissimmee.
The drive down with the kids (ages 9 and 5) wasn't that bad (even if the portable DVD player was on the fritz). We actually had a great time, singing along with the radio, listening to audio cassettes (my Nissan Quest doesn't have a CD player), stopping to eat at the Waffle House (discovered we don't care for the Huddle House that much), counting all the Cracker Barrel signs, etc., etc.
The drive back wasn't too bad (although Virginia feels that the longest state EVER!), even if we did come back to a driveway full of unplowed snow.
We're planning another WDW trip next February and we'll be driving again.