We drove down in 2003, and 2005. Now, we broke it up, becuase, well, the wife and I don't travel well in the car together.

When we planned it out, we figured it was about 16 hours for us, by using I-95.
In 03, I remember we got caught up in traffic in Baltimore, and again on the far side of DC. But that was all construction related. In 05, we had none of these problems.
We also travelled with young kids. In 03, DD wasn't even 1, and DS was 4. In 05, DD was 2.5 and DS was 6. We had to make pee stops/diaper changes, as well as food stops. We ended up both times, stopping in Florence, SC. I recall a lot of motels in that area, so it worked out well for us.
On our way back, I know we stopped in North Carolina somewhere, but don't remember where, as I think it was different places for each trip.