After the news about innovation vs rebranding, we have today an ATI/NVIDIA fight under Linux. The guys at HEXUS have selected 3 OpenGL applications: 2 benchmarks (Unigine Tropics and Lightsmark 2008) and one real world test: Enemy Territory: Quake Wars (easy!). The tested graphics cards are a Radeon HD 4870 (with Catalyst 9.4) and a GeForce GTX 260 (with ForceWare 180.37).
From the results, the graphics cards are pretty much equivalent with a slight lead for NVIDIA.