I can't believe you didn't get more replies to this! On behalf of the people in North Fulton County, I apologize! 
Alpharetta is awesome, and Roswell is too! Really, you can't go wrong with any of the areas in North Fulton County. I say this as someone who has lived here since September 2011 (I live in Roswell, but right on the border of Alpharetta and John's Creek). It's extremely family-friendly and safe, and the schools are some of the best in the state.
All that being said, it's an affluent area, so you are going to run into your fair share of McMansions and BMWs, but there are plenty of beautiful, tree-lined neighborhoods with down-to-earth families. Great parks, nature centers (the Chattahochee River is nearby), and family-friendly activities.
Check out http://www.gnfcc.com/ for more information about the area.
I am from Philadelphia orginally and have found that there are a lot of "transplants" in this area-from the Northeast, Midwest, and California, especially. There's a great deal of diversity in the Atlanta area, and a tremendous amount of culture, entertainment, and education in the metro area. Good food too! Obviously, I love it.
Feel free to PM me with additional questions. Good luck!
K
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