We are Canadians travelling to Hilton Head in October. We'll likely cross at Detroit. Do you have any for a good half-way point for an overnight stop? Any tips?
Thx.

Further than half, but if you make it to Charlotte, NC there are many nice hotels and restaurants. You have four to five hours left to HHI from Charlotte. Gets you to HHI around check in time the next day. On the south side of Charlotte off the Arrowood exit is a Courtyard that's in a good area. Additional benefit is that you are through Charlotte and can start without worrying about morning traffic.

we're about 2 hrs. from Detroit and then from Detroit, it's probably close to 10 hours to Charlotte. Although I like the idea of getting in earlier to HH, I think we want to avoid a 12 hour. drive day and split it up more equitably..any other suggestions?

Looking at the map, Charleston, W.Va., would be about halfway. You could overnight therebouts and then go ever-so-slightly out of your way to see the New River Gorge Bridge. It's on US19, but from I-77 you'd use US60 to reach it.
http://www.nps.gov/archive/neri/bridge.htm and http://www.nps.gov/neri/planyourvisit/crvc.htm

I don't think you would find that 12 hour drive too bad--it is all interstate and easy driving. I live in Charlotte and drive to southern Ohio regularly.
Charleston is 5 hours from Charlotte, just as an FYI. If you want to come a couple of hours south of that, there are a lot of motels at the Wytheville exit, but once south of that, it is all the way to Charlotte for much of anything. This is all on I77.
You might consider I75 to Knoxville, I40 to Asheville and I 26 south to Charleston and Hilton Head. This may be more direct for you. Knox to Ash is 2-3 hours. Asheville to the coast is about 6 I think. And then south to HHI.

Wytheville is a better stop than Charleston, WV. Two hours more, better divide on the ride. Not much there but hotels, but plenty to choose from. While the Knoxville to Ashville loop is a beautiful drive, you are adding about 3 hours to your trip.

If you want to drive more the first day, Mt. Airy is right off your route. It's the original "Mayberry" if you watched the Andy Griffith show (not sure you did in Canada).

If you want to sight-see a bit on the way down, detour a little bit in the NC mtns. Stop by Boone or Banner Elk or Asheville.

If I were going the drive, I'd take a detour into western PA because I want to see Frank Lloyd Wright's Fallingwater.

It depends if you just want a "pit stop" right off the interstate for a hotel or if you want to DO something on the way down.