I did a tour last month from Charleston, SC, to Norfolk, VA. The intent was to stay a near the coast as possible. Generally, US-17 is not very bike friendly, usually no shoulder. There was quite a bit of traffic in April; I imagine as the summer tourist season approaches, the traffic would be much heavie. A tourer we talked to said US-17 between Savannah and Charleston was terrible for riding -- lots of traffic and no shoulder.
Unfortunately, because of many rivers and inlets along the coast, we didn't have many options to US-17 until it went inland at Jacksonville, NC, and we stayed along the coast to get to the Outer Banks.
There are some stretches to avoid US-17 for a while -- Myrtle Beach & North Myrtle Beach, SC; NC-211 and US-421 south of Wilmington, NC; and NC-210 and NC-172 south of Jacksonville, NC.
If you aren't tied to the Adventure Cycleing route, the NC's Outer Banks make for great riding.