On my recent trip to Savannah, I spent the majority of Sunday walking around downtown. It seems that nationally Charleston and Savannah are thought of as very similar cities, but they are actually quite different. Savannah is further inland and built on a bluff, while Charleston is on a peninsula and barely built above sea level. Charleston is densely packed with narrow streets and row house after row house, while Savannah is configured on a planned grid with wide streets, squares, and long stretches of townhomes. The differences continue, but to me, the street level presence is one of the most profound distinctions between the two cities.
On another note, if you're in Savannah, check out shopSCAD. It has some pretty awesome works in it, including some inspiring photography books.