AMD generally has a good reputation right now. People know Athlon, people know 64 bit, and people like AMD. Even with Core 2 Duo coming out, most people still think AMD is the more powerful processor. But they also think it's faster because it's 64 bit, and don't realize Intel has had 64 bit for years as well.
ATI generally does not have a good brand reputation. People know nvidia and geforce, and know ati as the slow card, or the card with compatibility problems. I had to argue with some kid for hours that the x800xt I sold him was faster than his geforce 3 by a hell of a lot, and then he had to argue with his friend than an x800xt is a hell of a lot faster than a 9800pro. Stupid people.
Sad to see the ATI name die though, just as it was sad to see the 3dfx and Voodoo names die. Personally, I'd prefer keeping the ATI name over Radeon, but mainly because I've typically referred to the ATI cores as R300 or RV300 or whatever the code name is. Maybe Flipper, maybe Hollywood, maybe Xenos, but I've always related them together with the name ATI. Not to mention that I remember ATI before Radeon existed, and I know that ATI produces more than just radeons.
