ATLPaul has made some good suggestions. I would add Shout! to that, which is a midtown restaurant with an upscale hip-hop scene. The last time I was there Usher adn Rudy from the Cosby Show were eating there. Compound and Eleven50 are very diverse, as is B.E.D. in the Glenn Hotel downtown. None of these will be within walking distance of any hotel but should be less than $10 cab rides. You might want to check out the Glenn Hotel, a new upscale boutique hotel that is just gorgeous.
As far as restaurants go, almost all of the better restaurants in Atlanta are locally owned, so if you can give an idea as to type of cuisine, price range, etc., I can give more specific suggestions. However, I think you would really like Two Urban Licks.
The Grand Hyatt is a very nice hotel. If you're going to shop, Buckhead is the place to do it. It is just not the most popular place for bars or restaurants anymore. I generally recommend that people stay in midtown, but of the prior recommendations Eleven50 is the only club and Shout! the only restaurant that would be within walking distance of a 14th Street hotel like the Four Seasons.
