Family of 5 in a Grand Caravan, just got back yesterday. Spent 2 days down, 3 days back.
Sat Dec 21 - left Ottawa 3:47am in freezing rain. Took an extra hour to reach the border at 1,000 islands, but got there safe and the border bridges were open (I worried about all the ice). Just a few minutes later it changed to rain and the roads were wet but otherwise fine. Good the rest of the day until we hit about a 3-hour traffic delay around Washington (I-270, I-495, I-95). This was probably related to holiday shopping (I'm pretty sure). Still had some traffic on and off until we stopped in Lumberton, NC for the night.
Sun Dec 22 - left around 7:30am, traffic was manageable until I-4 in Orlando added 30-60 minutes as you got closer to International Drive area.
Thu Jan 2 - left around 8am and stopped in Fayetteville, NC for the night. No incidents.
Fri Jan 3 - left around 8am and stopped in Hershey, PA for the weekend. No incidents.
Sun Jan 5 - left around 8:30am and got back about 4pm. No incidents.
Overall, 3 points:
a) Although I don't regret doing a Christmas trip, I don't want to do it again. Just too busy everywhere, too much traffic everywhere.
b) I'd recommend the other route spending longer on I-81 to avoid even more of Washington (like Tower said).
c) None of us were that tired. Breaking the trip in 2 days seems about right (first day long, 2nd day short). Saved a TON of money on flights and rental car (esp. rental car cost over Christmas). I'd definitely drive again, just try going off season like we usually do.