I live in a very remote, rural area. I have as good of service with AT&T as I previously had with Verizon, the exception being that I don't drop calls nearly as often with AT&T. So slightly better, IMO. The Captivate performs well. Calls can get broken up at times, but when I have enough reception for calls, they sound crisp and clear.
I did try a booster as mentioned above. Installed properly and such. However, I found that the phone would take two attempts to do anything before the booster helped, for some reason. For instance, inside my house I can receive texts, but need to be by a window to send them. With the booster in place, I could attempt to send a text in the center of the house, and it would immediately fail. I could retry, and the booster would suddenly show activity, and the text would send. I don't know if this was just a booster issue. Probably so. I was using the zBoost dual-band. I'm almost always near a window, so I gave that up.
The biggest issue I have is that I'm nearly dead-center between three towers, so depending on which side of the house I'm on, the phone will start switching between the towers. This can cause a little delay. One of them is a 3g tower, the other two run Edge. I can't tell much of a difference there, but I rarely use it at home since I have wifi/broadband.
If you have any other questions regarding specifics on rural usage, feel free to PM me. I'll answer anything I can. I'm not checking back on the forums very often (seems like these posts keep getting pushed into subfolders anyway, and I don't have time to browse them all.)