just in general, traffic on the main streets in Nassau and on the island as a whole moves very quickly and bumper to bumper. People from larger US or European cities shouldn't have a problem coping with this, but Australians, Californians and people from smaller cities where the pace is slower should be ready for a challenge.
The Bahamas drives on the left, but that doesn't mean you will necesarily be getting British style cars, with the steering wheel on the opposite side. You could get one, but many more cars are in the American style, and the toll booths are built to accomodate them, not the British makes.
Gasoline is very expensive by American standards. When I was there, the price had come DOWN to $3.45 a gallon
Majestic Tours is a bad recommendation. The company is run down and owned by a racist who recently pulled a gun on a local black Doctor and his wife, threatening them because they were parked in front of his vehicle. The case is currently stalled in the Bahamas courts.
A better recommendation is Bahamas Experience. They are the tour company that services Atlantis and the only one, to my knowledge, that does a professional job.