A few years ago ATI couldn’t compete with nVidia. They made some good cards, but you always had too many small issues on this or that game and the drivers weren’t always good.
Last year ATI releases the 8400 series and it was suddenly the ONLY choice. The videocards were surprisingly cheap and the performance very solid. In the past the “best choice” would change every few months, today the best choice is still similar to the one of one year ago.
This is just the result of the Farcry 2 benchmark on my PC, with a standard 4850:
Average Framerate: 47.47
Max. Framerate: 62.76
Min. Framerate: 38.11
Average Framerate: 49.51
Max. Framerate: 66.72
Min. Framerate: 39.68
Average Framerate: 52.49
Max. Framerate: 67.24
Min. Framerate: 40.78
A few years ago when I ran a benchmark I was always getting slightly worse results every few months. This is not a huge improvement, but at least with every driver they make a small step forward and none backwards.
Between the first and second release they fixed some sharp choke points (the performance curve is now much smoother), between the second and third there was an overall increase. Not too bad considering this was already a very good card with solid performance when it launched.