There are two limo services from the Atlanta Airport to Macon. VIP Shuttle, (912) 788-3232, (912) 781-0000, or (800) 781-0006, works on a reservation system, although they have a semi-regular schedule to and from the airport. They don't have a website and the word is that they are somewhat less reliable than Groome.
Groome Transportation, (912) 471-1616, has a regular, hourly schedule to and from the airport; the schedule is on the website. Both services include the Crowne Plaza (official hotel) as a stop.
More information about transportation and directions to the hotel are forthcoming.